Methods for the extrusion of novel, highly plastic and moldable hydraulically settable compositions

ABSTRACT

Hydraulically settable mixtures and methods for extruding such mixtures into a variety of objects which are form-stable in the green state. High green strength is achieved by increasing the yield stress of the mixture while maintaining adequate extrudability. Optimizing the particle packing density while including a deficiency of water yields a hydraulically settable mixture which will flow under pressures typically associated with the extrusion of clay or plastic. In addition, a rheology-modifying agent can be added to increase the yield stress of the mixture while not significantly increasing the viscosity. The desired strength properties and other performance criteria of the final hardened extruded product are controlled by adding aggregates, fibers, a hydraulically settable binder, water, and other admixtures.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/019,151, entitled "Cementitious Materials For Use inPackaging Containers and Their Methods of Manufacture," and filed Feb.17, 1993, in the names of Per Just Andersen, Ph.D., and Simon K. Hodson,now U.S. Pat. No. 5,453,310. This application is also acontinuation-in-part of U.S. patent application Ser. No. 08/095,662,entitled "Hydraulically Settable Containers And Other Articles ForStoring, Dispensing, And Packaging Food And Beverages And Methods ForTheir Manufacture," and filed Jul. 20, 1993, in the names of Per JustAndersen, Ph.D., and Simon K. Hodson, now U.S. Pat. No. 5,385,764. Thisapplication is also a continuation-in-part of U.S. patent applicationSer. No. 08/101,500, entitled "Methods And Apparatus For ManufacturingMoldable Hydraulically Settable Sheets Used In Making Containers,Printed Materials, And Other Objects," and filed Aug. 3, 1993, in thenames of Per Just Andersen, Ph.D., and Simon K. Hodson. This applicationis also a continuation-in-part of U.S. patent application Ser. No.08/109,100, entitled "Design Optimized Compositions And Processes ForMicrostructurally Engineering Cementitious Mixtures," and filed Aug. 18,1993, in the names of Per Just Andersen, Ph.D. and Simon K. Hodson (nowabandoned). Each of these applications is also a continuation-in-part ofU.S. patent application Ser. No. 07/929,898, entitled "Cementitious FoodAnd Beverage Storage, Dispensing, And Packaging Containers And TheMethods Of Manufacturing Same," and filed Aug. 11, 1992, in the names ofPer Just Andersen, Ph.D., and Simon K. Hodson (now abandoned). Forpurposes of disclosure, each of these applications is incorporatedherein by specific reference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to hydraulically settable compositions andmethods used to extrude a wide variety of articles therefrom. Moreparticularly, the invention relates to hydraulically settable mixtureswhich have rheological properties that render them highly extrudableunder pressure and then form-stable immediately after they have beenextruded, even while in the green or unhardened state. The compositionsand methods allow for the extrusion of articles having thin walls,complicated shapes, or highly critical tolerances.

2. The Relevant Technology

Hydraulically settable materials such as those that contain ahydraulically settable binder like hydraulic cement or gypsum(hereinafter "hydraulically settable," "hydraulic," or "cementitious"compositions, materials, or mixtures) have been used for thousands ofyears to create useful, generally large, bulky structures that aredurable, strong, and relatively inexpensive. Hydraulic cement is ahydraulically settable binder derived from clay and limestone, whilegypsum is a naturally occurring mineral. Both are essentiallynondepletable.

Hydraulically settable materials are generally formed by mixing ahydraulically settable binder with water and usually some type ofaggregate to form a hydraulically settable mixture, which hardens into,e.g., concrete. Typically, a freshly mixed hydraulically settablemixture is fairly nonviscous, semi-fluid slurry, capable of being mixedand formed by hand. Because of its fluid-like nature, a hydraulicallysettable mixture is generally shaped by being poured into a mold, workedto eliminate large air pockets, and allowed to harden. If the surface ofthe concrete structure is to be exposed, such as on a concrete sidewalk,additional efforts are usually made to finish the surface to make itmore functional and to give it the desired surface characteristics.

Due to the high level of fluidity required for typical hydraulicallysettable mixtures to have adequate workability, the uses of concrete andother hydraulically settable materials have been limited to mainlysimple shapes which are generally large, heavy, and bulky, and whichrequire mechanical forces to retain their shape for an extended periodof time until sufficient hardening of the material has occurred. Anotheraspect of traditional hydraulically settable mixtures or slurries isthat they have little or no form-stability and are usually molded intothe final form by pouring the mixture into a space having externallysupported boundaries or walls. The problem of low form-stability isexacerbated by the lengthy curing and hardening times of most concretes.It may take days for most cementitious mixtures to have enough strengthto be demolded without being harmed, and weeks of wet curing to avoiddefects in the structural matrix.

The uses of hydraulically settable materials have also been limited bythe strength properties of concrete, namely, the high ratio ofcompressive strength to tensile strength, which is usually about 10:1.Fortunately, the strength limitations of concrete can usually beovercome by simply molding it into massive structures of enormous size.This is possible because of the extremely low cost of most concretes.The tensile strength of such massive structures has also been improvedby extensive use of metal reinforcing bars, or "rebar". However, the useof such hydraulically settable materials to make smaller, thinner-walledarticles has not been possible. The inability to use conventionalcementitious materials in the manufacture of small, thin-walled objectsis further complicated by the low strength per unit weight of thecomposition. In light of these factors, concrete is ideally suited formanufacturing large, bulky, and massive objects such as curbs, walkways,highways, bridges, buildings, aqueducts, sewer pipes, etc.

The long time period which must pass before typical hardenedcementitious products can be demolded greatly impedes the ability tomass produce cementitious objects and increases the cost of the finalproduct. The lengthy period before demolding also makes necessary theinitial investment of substantial amounts of money in order to purchasethe large number of molds required to mass produce a particular shape orarticle.

One way to avoid the added difficulties of having to demold the large,molded concrete forms would be to create a cementitious mixture withsufficient viscosity and cohesive strength so that it could be extrudedinto the desired shape without a mold and then maintain that shape(i.e., have form-stability). Extrusion of such a material would allowfor the continuous production of hydraulically settable objects withoutthe use of molds. The term "extrusion" has often been misleadingly usedin many patents and articles to denote processes for laying out acontinuous layer of concrete in a mold, which is then often compacted.Some have attempted to "extrude" cementitious mixtures, although theobjects extruded therefrom have mainly consisted of slab-like objects,relatively thick-walled pipes, and other structures of simple shape.

The extrusion processes that do not require a mold, mandrel, or othersupporting structure often involve the vertical (or downward) extrusionof materials to eliminate gravitational deformation of the structure.One problem with this is the discontinuous nature of the downwardextrusion process, since the extruded structures will eventually failunder their own weight. Another drawback has been that to obtainstructures that would maintain their shape and not slump when extrudedit has been necessary to use highly viscous cementitious materials thatrequire correspondingly high extrusion pressures and energies (such asvibration). In most cases, true form-stability (in which the object willnot slump without supporting mandrels, or in the vertical position) isnot achieved for a significant period of time, usually minutes or evenhours. The use of fibers to improve the material properties of the finalcured materials has further compounded the difficulties of the prior"extrusion" processes.

An example of an "extrudable" cementitious mixture can be found in U.S.Pat. No. 3,857,715 to Humphrey. Humphrey discloses a cementitiousmixture having a low water content, a carbohydrate additive (such asmolasses), and a high pH regulator, and which is said to be"self-supporting before being cured" (col. 3, lines 19-20), at leastwith respect to the objects which were reportedly formed by extrusion,namely "concrete block and pipe." (col. 1, line 7).

Nevertheless, Humphrey only partially solves the problems typicallyassociated with the molding of cementitious materials, which haveprevented their use in manufacturing a variety of useful objects whichmust presently be made from materials having superior properties ofstrength or moldability (such as paper, paperboard, plastic,polystyrene, or metal). The cementitious mixtures disclosed in Humphreyare only useful in the manufacture of relatively large, bulky objects ofextremely simple shape, such as concrete slabs or relativelythick-walled pipes (measured by the ratio of wall thickness to cavitycross-section). There is no indication that the compositions in Humphreycan be molded or extruded into more complicated structures or objectshaving relatively thin walls or highly critical tolerances.

In addition, the cementitious mixtures disclosed in Humphrey obtaintheir higher level of plastic-like behavior and form-stability throughthe use of sugar-based additives, together with a strong base, such asNaOH, and set accelerators, such as CaCl₂. The use of these additives inthese combinations diminishes the ultimate strength of the final curedcementitious product. Furthermore, in spite of the use of accelerators,the use of sugars to thicken the cementitious composition in Humphreygreatly retards the hydraulic reaction of the cement binder to the pointthat the extruded materials will sag or slump over time because of theinability of the mixtures to hydrate, and thereby solidify, in a timelymanner.

U.S. Pat. No. 5,047,086 to Hayakawa et al. discloses a cementitiouscomposition suitable for "extrusion molding" into the shape of boardshaving nailing and sawing characteristics similar to that of wood. Inorder to provide a composition with adequate extrudability, acellulose-based additive is blended with the cementitious mixture in anamount of 0.2% to 1% by weight, along with cellulosic fibers. However,Hayakawa et al. does not disclose or teach that the cementitious mixturedescribed therein would be useful in creating "extruded" articles otherthan flat boards. Nor does Hayakawa et al. anywhere indicate that thecementitious materials disclosed therein would have adequate strength,toughness, or other performance criteria that would allow it to beextruded into anything other than relatively thick boards having asimple, rectangular shape.

U.S. Pat. No. 4,588,443 to Bache discloses a densified cementitiousproduct known in the art as "DSP", which has superior compressivestrength properties and which is ideal for a number of uses requiringhigh compressive strength concrete. Within Bache are drawings showing acementitious mixture being "extruded" onto a form, or extruded to form acontinuous strip which is then spiral wound onto a mandrel to form apipe. However, nowhere does Bache teach that the cementitious materialsdisclosed therein might be extruded into more complicated structures,including multicellular or thin-walled objects, which will then maintaintheir shape without external support. Moreover, Bache fails to teach howto obtain a hydraulically settable mixture that is form-stable in thegreen state.

A major reason why cementitious materials, including those disclosed inHumphrey, Hayakawa et al., and Bache, are not capable of beingcontinuously extruded into complicated or thin-walled shapes is thetradeoff between workability and form-stability. The level ofworkability and flowability is substantially constant in all knowncementitious compositions throughout the three phases of extrusion: (1)placing the mixture into the extruder opening, (2) applying a pressureto the mixture to cause it to flow through the extruder, and (3)allowing the mixture to pass through a die orifice of the extruder.Although a stiff product might be greatly desired after step (3), itcannot be so stiff as to prevent the flowability of the mixture duringstep (2). Vibration of the mixture during steps (2) and (3) is oftennecessary in order for the mixture to flow or be "extruded."

In order for a hydraulically settable mixture to be capable of beingextruded using ordinary auger extruders used to extrude clay or plastic,the stiffness of the hydraulically settable mixture may not exceed thelevel which will prevent it from flowing through the extruder (or whichwould only yield a dry, noncohesive extrudate). However, the maximumallowable stiffness which will still allow the hydraulically settablemixture to flow through the extruder has heretofore yielded an extrudedproduct having inadequate form-stability for all but the simplestextruded articles, such as the cement slabs or thick-walled pipesdisclosed in Humphrey or Hayakawa et al. In most cases, the "extruded"cementitious mixture must be placed into a supporting form or onto amandrel in order to maintain the "extruded" material in the desiredshape, such as in Bache.

As the article being extruded becomes thinner-walled (by using a diehead with smaller openings), greater amounts of pressure and workabilityare required to overcome the increased resistance to flow of thematerial. However, greater cohesive strength and form-stability are alsorequired in order for an extruded material having thinner walls tomaintain its shape without external support. For this reason,cementitious mixtures have not been used to extrude anything but thesimplest of objects because they have not been able to simultaneouslyhave adequate extrudability while yielding a product with adequateform-stability.

Because of the tradeoff between workability (and extrudability) andform-stability, cementitious materials which are "extruded" horizontallyaccording to conventional methods generally must have a wall thicknessof about 25% of the cavity cross-section in the case of hollow objects(e.g., pipe), although vertically extruded objects can have a wallthickness to cavity cross-section up to about 1:16. Furthermore,conventional cementitious mixtures typically cannot be continuouslyextruded into objects that are very long. For example, the length towidth ratio of most extruded objects has typically peaked out at about5:1.

Even when fully cured, typical cementitious materials, even thosedisclosed in Humphrey, Hayakawa et al., and Bache, have relatively lowtensile and flexural strengths compared to other materials such aspaper, metal, or plastic. On the other hand, typical cementitiousmixtures, particularly those such as DSP, have a correspondingly highlevel of compressive strength to the point that it is unnecessary and,hence, inefficient. The relatively low tensile and flexural strengths,along with the problems with molding or forming cementitious mixtures,limit the use of cementitious mixtures to mainly large, bulky,heavyweight objects. Consequently, it would be a tremendous advancementin the art if a wider variety of articles having complex shapes orhighly critical tolerances could be manufactured from cementitiousmixtures, particularly in light of the extremely low cost ofcementitious materials compared to most other materials.

In fact, it is completely contrary to human experience to imagine themanufacture from hydraulically settable materials of small, thin-walled,relatively lightweight articles which are presently manufactured fromlighter weight, yet higher strength, materials such as paper,paperboard, plastic or other polymers, and aluminum or other metals. Itwould be an even greater achievement if such hydraulically settableobjects could be mass-produced in an economical and cost-effectivemanner.

Due to a growing awareness of the environmental harm caused by themassive use of paper, paperboard, plastic, metal, and wood tomanufacture the large quantities of mainly disposable items, there hasbeen an acute need to find environmentally sound substitutes for suchmaterials, such as hydraulically settable materials. In spite of suchpressures and long-felt need, the technology simply has not previouslyexisted for the economic and feasible production of hydraulicallysettable materials which could be substituted for paper, paperboard,plastic, polystyrene, metal, or wood in making a huge variety ofarticles. From an ecological standpoint, such a substitution ofmaterials would greatly reduce the amount of essentially nondegradable,environmentally harmful refuse which continues to build up within thenation's ever dwindling landfills.

Hydraulically settable materials are environmentally sound because theyessentially include aggregates consisting of natural geologic materials,such as sand and clay, which are bound together by the reaction productsof a hydraulically settable binder and water, which is also essentially"rocklike" from a structural, and especially chemical, viewpoint.Hydraulically settable materials have essentially the same chemical andstructural composition as the earth into which such materials mighteventually be disposed.

In addition, paper, plastic, metal, and wood are far more expensive thantypical hydraulically settable (including cementitious) materials.Because no rational business would ignore the economic benefit whichwould necessarily accrue from the substitution of radically cheaperhydraulically settable materials for paper, paperboard, plastic, metal,or wood materials, the failure to do so can only be explained by amarked absence of available technology to make the substitution.

Based on the foregoing, it would be an advancement in the art to providecompositions and methods that would allow the extrusion of hydraulicallysettable materials into articles and shapes which have heretofore beenimpossible because of the inherent strength and moldability limitationsof presently known hydraulically settable compositions.

It would yet be a tremendous advancement in the art to providecompositions and methods which result in the ability to extrudehydraulically settable products that have high strength in the greenstate. Such composition and methods would be particularly useful if theextruded products were immediately self-supporting without externalsupport.

It would further be an advancement in the art to provide hydraulicallysettable compositions which were highly plastic or moldable and whichwould readily maintain whatever shape into which they were extruded.

It would be an even greater advancement if such extruded hydraulicallysettable materials could be handled and transported using conventionalhandling means.

Still, it would be an advancement in the art to provide compositions andmethods which would yield a variety of thin-walled hydraulicallysettable articles. In addition, it would be a tremendous advancement inthe art to extrude hydraulically settable articles having highlycritical tolerances or dimensional preciseness.

It would yet be an advancement in the art to provide compositions andmethods for the extrusion of hydraulically settable articles having anincreased tensile strength to compressive strength ratio compared toconventional hydraulically settable materials.

It would be a tremendous advancement in the art to provide compositionsand methods which could be used to extrude hydraulically settablearticles that could take the place of articles presently manufacturedfrom other materials, such as paper, paperboard, plastic, clay, metal,or wood.

In addition, it would be a significant improvement in the art if suchcompositions and methods yielded hydraulically settable articles whichwere environmentally benign which essentially consisted of thecomponents found naturally within the earth.

It would be an advancement in the art to provide hydraulically settablecompositions that had the rheology and plastic-like behavior of claysuch that such compositions could be extruded using a clay extruder.

From a practical point of view, it would be a significant improvement ifsuch compositions and methods made possible the continuous manufactureof hydraulically settable articles at a cost and at production rates(i.e., high quantity) that are comparable or superior to the cost ofmanufacturing such articles from paper, paperboard, plastic, clay,metal, or wood.

Such compositions and methods are disclosed and claimed herein.

SUMMARY AND OBJECTS OF THE INVENTION

The present invention encompasses novel hydraulically settablecompositions and methods used for extruding a variety of objectstherefrom. Such compositions can generally be described asmulti-component, multi-scale, fiber-reinforced, micro-composites. Bycarefully incorporating a variety of different materials (includinghydraulically settable binders, inorganic aggregates, rheology-modifyingagents, and fibers) capable of imparting discrete yet synergisticallyrelated properties, it is possible to create a unique class or range ofmicro-composites having remarkable properties of strength, toughness,environmental soundness, mass-producibility, and low cost.

These compositions can be extruded into a variety of shapes, rangingfrom the very simple to articles having highly critical tolerances andthin walls. Because of the continuous nature of the extrusion process,such articles can be produced in a very cost-effective and economicalmanner. Moreover, the hydraulically settable materials of the presentinvention are environmentally neutral and comprise materials that haveessentially the same qualities and characteristics as the earth, as domost hydraulically settable materials.

Using a microstructural engineering approach, one can design into ahydraulically settable mixture the desired properties of rheology(including workability, yield stress, viscosity, and green strength) andfinal cured strength. In addition, properties such as high particlepacking density, toughness, tensile strength, and elongation can also bedesigned into the mixture beforehand.

In order to solve the problems inherent in typical hydraulicallysettable mixtures, namely the tradeoff between good workability and highgreen strength, the present invention makes possible the ability to havea high degree of workability during the molding process and yet achieveform-stability immediately or shortly after the extrusion process. Thisis preferably accomplished by creating a hydraulically settable mixturehaving a relatively high yield stress and an apparently low viscosity,particularly when exposed to higher pressures during the extrusionprocess.

To achieve high extrudability and high green strength (i.e.,form-stability), the hydraulically settable mixtures of the presentinvention generally rely on the heretofore perceived nonanalogousproperties of particle packing optimization and water deficiency tocreate a relatively stiff material with high yield stress, but which hashigh workability when subjected to the increased pressures and shearrates associated with extrusion. By choosing aggregates selected to havevarying but carefully chosen diameters, particle size distribution("PSD"), and packing density, it is possible to reduce the amount ofinterstitial space between the particles by filling the spaces betweenthe larger particles with smaller particles, and in turn filling thespaces formed by the smaller particles by yet smaller particles. In thisway, it is possible to achieve particle packing densities in the rangefrom about 65% to even as high as about 99%. That is, the volume of thedry hydraulically settable mixture will include from about 65% to about99% solid material, and only from about 35% to as low as about 1%interstitial space.

By carefully controlling how much water is added to the hydraulicallysettable mixture, one can create a mixture having a carefully chosendegree of "water deficiency." As discussed in greater detail below, itshould be understood that water is added to a hydraulically settablemixture for essentially two reasons: (1) to chemically react with (or"hydrate") the hydraulically settable binder and (2) to fill the voidsbetween the particles in order to reduce the friction between theparticles and lubricate them in order to give the mixture adequateplasticity and cohesion. If the amount of water is deficient, there willbe greater friction between the particles, thereby resulting in astiffer material. Depending on the amount of water or other additives(such as dispersants, which can be added to lubricate or disperse theparticles), one skilled in the art can carefully control the rheology inorder to create the desired level of workability under pressure.

It should be understood that a mixture having greater packing densitywill require much less water to fill the interstitial voids.Consequently, the amount of water added to create a desired level ofwater deficiency must be carefully calculated before the water is added,the amount of water being based primarily upon the particle packingefficiency and the anticipated compression of the extrusion process.

Once a suitable hydraulically settable mixture has been created, it isplaced in an extruder and then subjected to pressure. The resultingcompression increases the packing density by forcing the particlestogether, which in turn decreases the volume of interstitial spacebetween the individual particles of the mixture. This decreases the"effective" level of water deficiency, which increases the amount ofwater available to lubricate the particles (as well as to lubricate themovement of the hydraulically settable mixture through the extruderdie), whereupon the hydraulically settable mixture has greaterworkability and is able to flow. In addition, compressing the mixtureduring extrusion also creates a thin film of water between the extruderdie and the mixture, which lubricates the surface between the die andmixture. The extruder die may also be heated in order to create a steam"cushion" or barrier between the extruded hydraulically settable mixtureand the extruder die, thereby reducing the friction and increasing theease of extrusion. Thereafter, the internally formed capillaries ormenisci caused by compressing the mixture creates internal cohesionforces that give the mixture improved form-stability after extrusion.

The high level of workability and flowability of the mixture while underpressure allows it to be extruded through an orifice of an extruder dieinto the desired article or shape. The ability of the hydraulicallysettable mixture to be extruded and have good form-stability may beaccomplished in one of two ways. First, because most of thehydraulically settable mixtures of the present invention approximatelybehave as a Bingham fluid, or pseudo-plastic body, the viscosity of themixture will decrease as the critical shear rate in the form of appliedpressure is exceeded. In other words, the hydraulically settablemixtures of the present invention usually experience "shear thinning" asthe pressure (and hence the shear) is increased, such as by using anextruder capable of applying high pressure. Hence, by applying highpressures, most hydraulically settable mixtures of the present inventioncan be extruded.

Instead of, or in addition to the application of high pressure, it mayalso be advantageous to design a hydraulically settable mixture that hasthe lowest possible ratio of viscosity to yield stress. As the viscosityis lowered the amount of stress above the materials yield stressnecessary to cause the mixture to flow decreases. This strategy isespecially useful where lower pressure extrusion is desired.

Upon being extruded, the hydraulically settable mixture will no longerbe exposed to the compressive and shear forces of the extruder, and themixture will then revert to its pre-compression stage of greaterstiffness and higher viscosity. Consequently, the extruded shape orarticle will exhibit a high level of green strength and form-stability.The amount of green strength achieved by the compositions and methods ofthe present invention far exceeds that which has been obtained usingprevious cementitious compositions and methods.

The hydraulically settable compositions of the present invention mayalso include other components besides a hydraulically settable binder,water, and aggregates such as rheology-modifying agents, dispersants,and fibers. Rheology-modifying agents can be added to increase the yieldstress, cohesive strength, and plastic-like behavior of thehydraulically settable mixture, while dispersants can be added in orderto obtain a mixture having similar flow properties while including lesswater. Fibers are usually added to increase the toughness and tensile,flexural and, sometimes, even the compressive strength of the finalcured product.

More particularly, rheology-modifying agents increase the "plastic-like"behavior, or the ability of the mixture to retain its shape when moldedor extruded. Suitable rheology-modifying agents include a variety ofcellulose-, starch-, and protein-based materials, which can be ionic ornonionic, and which act by bridging the individual hydraulicallysettable binder particles and other particles in the matrix together.

By increasing the "plastic-like" consistency of the hydraulicallysettable mixture, the rheology-modifying agent also increases theability to extrude an article having high form-stability. (Gypsumhemihydrate may also be added in order to increase the form-stabilitydue to its rapid reaction with water, thereby reducing the amount ofcapillary water present in the hydraulically settable mixture in a shortperiod of time. In this way gypsum hemihydrate may act as arheology-modifying agent in some cases.)

Dispersants, on the other hand, act to decrease the viscosity and yieldstress of the mixture by dispersing the individual hydraulicallysettable binder particles. This allows for the use of less water whilemaintaining adequate levels of workability, which allows for greaterwater deficiency. Suitable dispersants include any material which can beadsorbed onto the surface of the hydraulically settable binder particlesand which act to disperse the particles, usually by creating a negativeelectrical charge on the particle surface or into the near colloiddouble layer. Fillers such as kaolin, mica, calcium carbonate, orbentonite also become highly dispersed by the use of dispersants.

However, in the case where both a dispersant and a rheology-modifyingagent are used, it will usually be advantageous to add the dispersantfirst and the rheology-modifying agent second in order to obtain thebeneficial effects of each. Otherwise, if the rheology-modifying isfirst adsorbed by the binder particles it will form a protectivecolloid, which will greatly inhibit the adsorption of the dispersant bythe particles, thereby limiting the dispersing effect of the dispersantwithin the hydraulically settable mixture.

In addition to adding aggregates having various diameters, shapes,sizes, and properties (e.g., specific gravity, bulk density,morphology), it might be desired to include aggregates having differentstrength and insulation properties. In this way, the hydraulicallysettable mixture can be optimized both from the standpoint of thedesired rheology or flow properties useful in the extrusion process aswell as the final properties of the cured material.

Using the compositions and processes described above, it has beenpossible to extrude a wide variety of different articles having varyingshapes, sizes, thicknesses, and other properties. Such extruded objectsor shapes include flat sheets, rods, bars, rectangular bars, boards,"I-beams," "two-by-fours," honeycomb and other multicellular structures,corrugated structures, pencils, cylinders, peanut-shaped packingmaterials, pipes, "spaghetti" or other packaging or filler material,window frames, bricks, roofing tiles, or factory panels. It has beenpossible to maintain highly critical tolerances of these extrudedobjects, where necessary, because of the workability and high greenstrength of the hydraulically settable mixtures disclosed and claimedherein.

These objects have properties which are similar, and even superior, tosimilar objects made from other materials such as paper, plastic,paperboard, polystyrene, wood, clay, or metal. However, hydraulicallysettable materials have the advantage that they are often much lower incost than these other materials. In addition, the hydraulically settablematerials made according to the present invention are much moreenvironmentally benign than presently used materials and do not requirefurther processing after extrusion.

From the foregoing, it would be appreciated that an object of thepresent invention is to provide and teach the microstructuralengineering design process for obtaining highly plastic, extrudablehydraulically settable mixtures that can be extruded into a variety ofarticles not previously obtainable using hydraulically settable mixturesof the prior art. This is accomplished by creating hydraulicallysettable mixtures having high yield stress and sufficiently lowviscosity under pressure so that the mixture will flow during theextrusion process but have sufficient cohesiveness to be immediatelyform-stable and strong enough to maintain its shape without externalsupport after being extruded, even while in a green state.

Another object of the present invention is to provide hydraulicallysettable compositions which are highly plastic or moldable and whichwill readily maintain whatever shape into which they are extruded. Yetanother object is to provide hydraulically settable materials andmethods in order to extrude articles that can be handled and transportedusing conventional means.

It is a further object of the present invention to provide hydraulicallysettable compositions and methods which yield a variety of thin-walledarticles including articles that require highly critical tolerances ordimensional preciseness.

Yet another object of the present invention is to provide compositionsand methods for the extrusion of hydraulically settable articles havingan increased tensile strength to compressive strength ratio compared toconventional hydraulically settable materials.

A still further object and feature of the present invention is thedevelopment of hydraulically settable compositions and methods used toextrude a variety of articles that can take the place of articlespresently manufactured from other materials, such as paper, paperboard,plastic, wood, clay, or metal.

Another object and feature of the present invention is the developmentof compositions and methods that yield hydraulically settable articleswhich are environmentally benign and which essentially consist of thecomponents found naturally within the earth.

Yet another object of the present invention is to provide hydraulicallysettable compositions that have the rheology and plastic-like behaviorof clay, such that they can be extruded using a clay extruder.

A still further object and feature of the present invention is thedevelopment of hydraulically settable compositions and methods whichmake possible the manufacture of a variety of hydraulically settablearticles at a cost and at production rates that are comparable orsuperior to the cost of manufacturing such articles from paper,paperboard, plastic, wood, clay or metal.

These and other objects and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto a specific embodiment thereof, which is illustrated in the appendeddrawings. Understanding that these drawings depict only a typicalembodiment of the invention and are not, therefore, to be consideredlimiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a greatly enlarged elevational cross-section view of thearrangement of particles within a hydraulically settable mixture havinga moderately high natural particle packing density of 70%.

FIG. 2 is a greatly enlarged elevational cross-section view of themixture illustrated in FIG. 1, together with a corresponding graphquantifying the volume occupied by the particles and the volume occupiedby the interstitial voids between the particles.

FIG. 3 is a greatly enlarged elevational cross-section view of themixture illustrated in FIG. 1 to which a quantity of water equaling thevolume of interstitial voids has been added, together with acorresponding graph quantifying the volume occupied by the particles andthe volume occupied by the water between the particles.

FIG. 4 is a greatly enlarged elevational cross-section view of themixture illustrated in FIG. 1 to which a quantity of water less than thevolume of interstitial voids has been added to form a water deficientmixture, together with a corresponding graph quantifying the volumeoccupied by the particles, the volume occupied by the water between theparticles, and the volume occupied by the interstitial voids that yetremain between the particles.

FIG. 5 is a greatly enlarged elevational cross-section view of themixture illustrated in FIG. 4 upon which a compressive force (i.e.,pressure) has been applied sufficient to force the particles into a moreclosely packed arrangement, together with a corresponding graphquantifying the volume occupied by the particles, the volume occupied bythe water between the particles, and the lesser volume occupied by theinterstitial voids that yet remain between the particles.

FIG. 6 is a cross-section view of an auger extruder.

FIG. 7 is a cross-section view of a piston extruder.

FIGS. 8A-8E show graphs illustrating the relationship between strength,particle packing density, and water content of hydraulically settablemixtures that have 14.3% portland cement, 85.7% aggregate, and varyingwater deficiencies.

FIGS. 9A-9E show graphs illustrating the relationship between strength,particle packing density, and water content of hydraulically settablemixtures that have 25% portland cement, 75% aggregate, and varying waterdeficiencies.

FIGS. 10A-10E show graphs illustrating the relationship betweenstrength, particle packing density, and water content of hydraulicallysettable mixtures that have 33.3% portland cement, 66.7% aggregate, andvarying water deficiencies.

FIGS. 11A-11E show graphs illustrating the relationship betweenstrength, particle packing density, and water content of hydraulicallysettable mixtures that have 40% portland cement, 60% aggregate, andvarying water deficiencies.

FIGS. 12A-12E show graphs illustrating the relationship betweenstrength, particle packing density, and water content of hydraulicallysettable mixtures that have 45.5% portland cement, 54.5% aggregate, andvarying water deficiencies.

FIGS. 13A-13E show graphs illustrating the relationship betweenstrength, particle packing density, and water content of hydraulicallysettable mixtures that have 50% portland cement, 50% aggregate, andvarying water deficiencies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention includes novel compositions and methods forobtaining highly plastic, extrudable hydraulically settable mixtures,which can be extruded into a variety of articles, including those whichhave thin walls, complicated shapes, and/or highly critical tolerances.In addition, relatively large, thick-walled objects such as"two-by-fours" or other structural objects can also be efficientlyextruded using the compositions of the present invention. Such extrudedobjects are immediately (or in a manner of seconds) form-stable uponbeing extruded.

The novel extrudable compositions can generally be described asmulti-component, multi-scale, fiber-reinforced, micro-composites. Bycarefully incorporating a variety of different materials (includinginorganics and fibers) capable of imparting discrete yet synergisticallyrelated properties, it is possible to create a unique class or range ofmicro-composites having remarkable properties of strength, toughness,environmental soundness, mass-producibility, and low cost.

The term "multi-component" refers to the fact that the extrudablehydraulically settable materials of the present invention typicallyinclude three or more chemically or physically distinct materials orphases, such as fibers, inorganic aggregate materials, organic aggregatematerials, hydraulically settable materials, organic rheology-modifyingagents, dispersants, water, and other liquids. Each of these broadcategories of materials imparts one or more unique properties to thefinal article extruded therefrom (as well as the mixture used to formthe article). Within these broad categories it is possible to furtherinclude different components (such as two or more inorganic aggregatesor fibers) which can impart different, yet complementary, properties tothe extruded article. This allows for the specific engineering ofdesired properties within the article in conjunction the extrusionprocess.

The term "multi-scale" refers to the fact that the compositions andmaterials of the present invention are definable at different levels orscales. Specifically, within the hydraulically settable materials of thepresent invention there is typically a macro-component composition inthe range from about 0.01 mm to as high as about 10 mm, amicro-component composition in the range of about 10 nanometers to about10 microns, and a submicron component. Although these levels may not befractal, they are usually very similar to each other, and homogeneousand uniform within each level.

The term "fiber-reinforced" is self-explanatory, although the key termis "reinforced", which clearly distinguishes the hydraulically settablematerial of the present invention from other conventional materials usedto manufacture a variety of articles, such as conventional paper orpaper products. Conventional paper relies on "web" physics, orintertwining of fibers, to provide the structural matrix and mass, aswell as the binding, of the paper. However, the matrix of thehydraulically settable materials of the present invention relies on thebond or interaction between the hydraulically settable binder, inorganicaggregate, the rheology-modifying agent, and the fibers. The fibers actprimarily as a reinforcing component to specifically add ductility,tensile strength, and flexibility.

Finally, the term "micro-composite" refers to the fact that thehydraulically settable materials are not merely a compound or mixturebut a designed matrix of specific, discrete materials on a micro-level,which are of different sizes, shapes, and chemical make-up. Thematerials are sufficiently well bound and interactive so that the uniqueproperties of each are fully evidenced in the final composite (e.g., thetensile strength of the matrix has a direct correlation to the tensilestrength of the fibrous component; the insulation of the matrix has adirect correlation to the total porosity and insulative character of theaggregate material; etc.).

In light of these definitions and principles, materials that include ahydraulically settable binder, an inorganic aggregate, water,(optionally) fibers (both organic and inorganic), and (optionally) anorganic rheology-modifying agent can be combined and extruded into avariety of articles. Such articles can have a variety of differentstrength, toughness, and density characteristics, and can have highlycritical tolerances. This allows the hydraulically settable materials ofthe present invention to be extruded (and, hence, mass produced) into avariety of articles presently made from, e.g., plastic, paperboard,metal, wood, glass, or polystyrene.

As described more fully hereinafter, the basic parameters of thehydraulically settable mixtures of the present invention include (1) theparticle packing density, (2) the amount of hydraulically settablebinder (usually hydraulic cement), (3) the amount of water, (4) theextrusion pressure, (5) the rheology (including the yield stress andgreen strength), and (6) the strength of the final cured product(including compressive and tensile strengths).

I. GENERAL DISCUSSION A. General Description of the Extrusion Process

Hydraulically settable products, including cementitious materials andthe methods of utilizing them, have been known for millennia. The typesof cementitious or other hydraulically settable products that have beenmade are various and numerous, although they share the common quality ofgenerally being large and bulky. In particular, cementitious objectsgenerally require significant size and mass in order to achieve thedesired strength and other performance criteria. Typical cementitiousmaterials also require relatively extensive setting and curing timesbefore they can be demolded. The moldability and/or extrudability ofmost hydraulically settable mixtures is generally limited by thetradeoff between workability and form-stability. Increasing one usuallydecreases the other, leaving only a narrow range of acceptablerheologies.

The present invention overcomes this tradeoff between extrudability andform-stability by creating a highly plastic and cohesive hydraulicallysettable mixture that is form-stable immediately or shortly after beingextruded. The term "plastic" refers to a hydraulically settable mixturethat is workable, which will flow under pressure, and which hassufficient cohesive strength so as to be form-stable in the green state(green strength or form-stability is either immediate or within a matterof seconds).

The unique properties of the hydraulically settable mixtures madeaccording to the present invention result from carefully controlledrheology, preferably by optimizing the particle packing density, asdescribed more fully below, coupled with a deficiency of water. Thedeficiency of water yields a relatively stiff, or highly viscous,hydraulically settable mixture because there is insufficient water tocompletely fill the interstices between the particles, leavinginsufficient water to fully lubricate the particles. In cases wherethere is very low initial water, the hydraulically settable mixture mayconsist of dry-looking granulates that lack cohesion and do not holdtogether as a single mass.

However, by exposing the water deficient mixture to increased mechanicalpressure by an auger or piston extruder, as well as by applying a vacuumto the mixture in order to substantially evacuate the air within theinterstitial space, the particles within the hydraulically settablemixture compress together, thereby increasing their packing density.This in turn reduces the effective water deficiency, thus allowing thewater to more completely fill the interstices between the more denselypacked particles. The apparent increase in the water that is availableto fill the interstices better lubricates the particles, reduces theinterparticulate friction, and allows the mixture to flow more easily bytemporarily decreasing the yield stress. In addition, vibrating themixture may also decrease the viscosity of a water deficient mixture.

Upon exiting the die, the reduction in pressure exerted on thehydraulically settable mixture allows the material to expand slightlyand return to a slightly less optimized state of particle packing. Thisin turn creates a partial vacuum or negative pressure within thecapillaries and strong meniscus forces are created that hold thehydraulically settable material together. The sudden lack of pressure(and lower shear rate) increases the viscosity of the material which,together with a high yield stress at the zero sheer rate, reduces theamount of water available to lubricate the particles, and results in animmediate increase in form-stability.

The rheology of the hydraulically settable mixture may also beinfluenced by other additives within the cementitious mixture, such ascellulose-, starch, or protein-based or synthetic organicrheology-modifying agents, which increase the yield stress of themixture while not significantly increasing or decreasing the viscosityto the point of unworkability. Under the high shear conditions withineither an auger or piston extruder, the higher yield stress is overcome,the plastic viscosity is temporarily lowered, and the mixture has atemporary increase in its ability to flow. Once the hydraulicallysettable material has been extruded and the shear forces have beenremoved, the rheology-modifying agent aids in creating a more cohesive,form-stable extruded product. Hence, the rheology-modifying agent helpsto create a hydraulically settable mixture that exhibits sheer thinning,thixotropic, or pseudo-plastic behavior, that is, a material which hasan apparent decrease in viscosity when subjected to shear forces,including pressure and vibration.

In addition to imparting desired rheological properties to the mixture,optimizing the particle packing within the mixture greatly increases thefinal strength of the cured product by reducing the amount of water andair within the hydraulically settable matrix. According to the StrengthEquation below, the compressive strength of a cured cementitious producthas been found to be inversely proportional to the amount of added waterand interstitial air (σ is the strength of the cured cementitiousproduct; k represents the highest possible theoretical strength,assuming no interstitial water or air, and is usually about 300-500 MPa,although it may be as high as 800 MPa in some cases, such as where theextruded article is cured by autoclaving; V_(c) is the volume of cement;V_(w) is the volume of water; and V_(a) is the volume of air orinterstitial space within a cementitious mixture):

    σ=k[V.sub.c /(V.sub.c +V.sub.w +V.sub.a)].sup.2 MPa

In normal, uncompacted cement paste, k=340 MPa, while in a highlycompacted system k=500 MPa. The size of k therefore depends on theprocessing technique, but is constant for the same technique. Ingeneral, reducing the amount of air and water within the hydraulicallysettable mixture will both increase the strength of the final curedmaterial. Both can be reduced while also improving the workability ofthe hydraulically settable mixture by increasing the particle packingdensity, as set forth more fully below. In addition, increasing theextrusion pressure and attendant compaction during the extrusion processcan also greatly reduce the amount of interstitial air, whilemaintaining adequate flowability where a higher water deficiency (lesswater) is used.

In cases where the particle packing density of the hydraulicallysettable mixture has been optimized to the higher end of the rangesdiscussed herein, a relatively high extrusion pressure capable ofeliminating most of the interstitial air is used, and very little wateris added initially, articles of manufacture having a hydraulicallysettable matrix can be extruded which have compressive strengths higherthan 500 MPa, even approaching 800 MPa if autoclaved, for example.

It is true that high strength concrete products have been made in alaboratory setting which have low water and low interstitial air.However, they are generally formed by isostatic compaction (often drypacked) under extreme pressures, usually by means of high pressuremolding greater than about 70 MPa. However, these methods are notadaptable to the economical mass production of cementitious materials,nor do they allow for the molding of anything but the simplest, mostrudimentary forms. They certainly do not allow for the continuousformation by extrusion of large volumes of form-stable hydraulicallysettable articles such as are possible using the compositions andmethods of the present invention. Moreover, extrusion provides a morecontinuous method for mass producing certain articles, such as thosethat are relatively long and narrow and have a constant cross-sectionalshape and dimension, compared to conventional molding processes.

It may also be desirable to co-extrude the hydraulically settablemixture with other materials in order to obtain, e.g., a laminatestructure or an extruded product with other materials impregnated withinor extruded over the surface of the hydraulically settable matrix.Things which may be co-extruded with the extrudable hydraulicallysettable mixtures of the present invention include another hydraulicallysettable mixture (often having different or complementary properties), afibrous mat, continuous fibers, graphite (to form pencils), coatingmaterials, polymers, clays, continuous fibers, or strips, wires, orsheets of almost any other material (such as metal). It has been foundthat by joining together, for example, a hydraulically settable sheetand a fibrous mat by co-extrusion the final product exhibits synergisticresults of strength, toughness, and other desirable properties.

After the hydraulically settable mixture has been extruded into thedesired shape, it may be allowed to harden in the extruded shape. Thehardening process may be accelerated by heating the object, such bymeans of heating under controlled high relative humidity or highpressure autoclaving. Alternatively, the extruded shape may further bealtered or manipulated, such as by passing an extruded sheet between apair of rollers in order to reduce the thickness of the sheet and/orimprove the surface quality of the sheet. The extruded object may alsobe curved, bent, cut, or further molded using any known molding processinto a wide variety of other objects or shapes.

B. Extruded Shapes and Articles

Terms such as "extruded shape" or "extruded article," as used in thisspecification and the appended claims, are intended to include any knownor future designed shape or article extruded using the compositions andmethods of the present invention. An illustrative, yet by no meansexhaustive, list of the shapes or objects which may be formed accordingto the present invention includes rods, bars, concrete rebars, pipes,cylinders, honeycomb and other multicellular structures, corrugatedstructures, boards, I-beams, "two-by-fours", flat sheets (rangingupwardly from 0.05 mm in thickness), "spaghetti" or other packaging orfiller materials, straws, window frames, bricks, roofing tiles, andpencils and other marking implements.

In addition, the terms "extruded article" or "extruded shape" areintended to also include all precursor shapes or articles that areinitially formed by extruding the compositions of the present inventionand then manipulated, augmented, or otherwise formed into other shapesor articles. For example, an extruded bar or pipe which is initiallystraight might be curved into a curved bar. Both straight and curvedbars or pipes are within the purview of the present invention and areintended to fall within the definition of an "extruded article" or"extruded shape."

These terms are also intended to include any extruded article or shapewhich is intended to be incorporated into any other article, whether ornot such article is also within the scope of this patent. While thecombination of extruded articles, or the combination of an extrudedarticle and any other article, might have independently patentablefeatures, the subpart obtained by the extrusion of the hydraulicallysettable mixtures made according to the present invention is intended tofall within the terms "extruded object" or extruded article," as wouldany combination of subparts.

C. Microstructural Engineering Design

As mentioned above, the compositions used to make the extrudablehydraulically settable mixtures of the present invention have beendeveloped from the perspective of a microstructural engineering andmaterials science approach in order to build into the micro structure ofthe hydraulically settable matrix certain desired, predeterminedproperties, while at the same time remaining cognizant of costs andother manufacturing complications. Furthermore, this microstructuralengineering analysis approach, in contrast to the traditionaltrial-and-error, mix-and-test approach, has resulted in the ability todesign hydraulically settable materials with those properties ofstrength, weight, insulation, cost, and environmental neutrality thatare necessary in order to extrude a wide variety of hydraulicallysettable objects in a significantly more efficient manner thanpreviously possible.

The number of different raw materials available to engineer a specificproduct is enormous, with estimates ranging from between fifty thousandand eighty thousand. They can be drawn from such disparately broadclasses as metals, polymers, elastomers, ceramics, glasses, composites,and cements. Within a given class, there is some commonality inproperties, processing, and use-patterns. Ceramics, for instance, have ahigh modulus of elasticity, while polymers have a low modulus; metalscan be shaped by casting and forging, while composites require lay-up orspecial molding techniques; hydraulically settable materials, includingthose made from hydraulic cements historically have low flexuralstrength, while elastomers have high flexural strength.

However, compartmentalization of material properties has its dangers; itcan lead to specialization (the metallurgist who knows nothing ofceramics) and to conservative thinking ("we use steel because that iswhat we have always used"). In part, it is this specialization andconservative thinking that has limited the consideration of usinghydraulically settable materials for a variety of products such asextruded shapes, particularly those with relatively thin walls,complicated shape or highly critical tolerances.

Nevertheless, once it is realized that hydraulically settable materialshave such a wide utility and can be microstructurally designed andengineered, then their applicability to a variety of possible productsbecomes obvious. Hydraulically settable materials have an additionaladvantage over other conventional materials in that they gain theirproperties under relatively gentle and nondamaging conditions. (Othermaterials require high energy, severe heat, or harsh chemical processingthat significantly affects the material components.) Therefore, manynonhydraulically settable materials can be incorporated intohydraulically settable materials without damage and with surprisingsynergistic properties or results if properly designed and engineered.

The design of the compositions of the present invention has beendeveloped and narrowed, first by primary constraints dictated by thedesign, and then by seeking the subset of materials which maximizes theperformance of the components. At all times during the process, however,it is important to realize the necessity of designing products which canbe manufactured in a cost-competitive process.

Primary constraints in materials selection are imposed bycharacteristics of the design of a component which are critical to asuccessful product. With respect to an extruded object, those primaryconstraints include desired weight and desired strength (bothcompressive and tensile), toughness, and other performance criteriarequirements, while simultaneously keeping the costs comparable totheir, e.g., paper, plastic, or metal counterparts.

As discussed above, one of the problems with hydraulically settablematerials in the past has been that they are typically poured into aform, worked, and then allowed to set, harden, and cure over a longperiod of time--even days or weeks. Experts generally agree that ittakes at least one month for traditional concrete products to reachtheir maximum strength. Even with expensive "set accelerators," thisstrength gain occurs over a period of days. Such time periods areusually impractical for the economic mass production of the extrudedobjects contemplated by the present invention.

As a result, an important feature of the present invention is that whenthe hydraulically settable mixture is extruded into the desired shape orarticle, it will maintain its shape (i.e., support its own weightsubject to minor forces, such as gravity and movement through theprocessing equipment) in the green state without external support.Further, from a manufacturing perspective, in order for production to beeconomical, it is important that the extruded object rapidly (in amatter of minutes or even seconds) achieve sufficient strength so thatit can be handled using ordinary manufacturing procedures, even thoughthe hydraulically settable mixture may still be in a green state and notfully hardened.

Another advantage of the microstructural engineering and materialsscience approach of the present invention is the ability to developcompositions in which cross-sections of the structural matrix are morehomogeneous than have been typically achieved in the prior art. Ideally,when any two given samples of about 1-2 mm³ of the hydraulicallysettable matrix are taken, they will have substantially similar amountsof hydraulically settable binder particles, hydraulically settablebinder gel, aggregates, fibers, rheology-modifying agents, and any otheradditives.

In its simplest form, the process of using a materials science analysisin microstructurally engineering and designing a hydraulically settablematerial comprises characterizing, analyzing, and modifying (ifnecessary): (a) the aggregates, (b) the particle packing, (c) the systemrheology, and (d) the processing and energy of the manufacturing system.In characterizing the aggregates, the average particle size isdetermined, the natural packing density of the particles (which is afunction of the actual particle sizes and morphology) is determined, andthe strength of the particles is ascertained. (Unreacted or previouslyreacted hydraulically settable binder particles may be considered to bean aggregate.)

With this information, the particle packing can be predicted accordingto mathematical models. It has been established that the particlepacking is a primary factor for designing desired requirements of theultimate product, such as workability, form-stability, shrinkage, bulkdensity, insulative capabilities, tensile, compressive, and flexuralstrengths, elasticity, durability, and cost optimization. The particlepacking is affected not only by the particle and aggregatecharacterization, but also by the amount of water and its relationshipto the interstitial void volume of the packed aggregates.

System rheology is a function of both macro-rheology and micro-rheology.The macro-rheology is the relationship of the solid particles withrespect to each other as defined by the particle packing. Themicro-rheology is a function of the lubricant fraction of the system. Bymodification of the lubricants (which may be water, rheology-modifyingagents, plasticizers, dispersants, other materials, or a combination ofthese), the viscosity and yield stress can be modified. Themicro-rheology can also be modified physically by changing the shape andsize of the particles, e.g., the use of chopped fibers, plate-like mica,round-shaped silica fume, rhombic fused silica, or crushed, angular, orgranular hydrated binder particles, each of which will interact with thelubricants differently.

Finally, the manufacturing processing can be modified to manipulate thebalance between workability and form-stability. In general, lowering theviscosity of the mixture increases the workability, while increasing theyield stress increases the form-stability of the extruded material. Asapplied to the present invention, it is generally optimal to maintain aminimum desired yield stress while minimizing the viscosity. Molding ordeformation of the material only occurs when a force greater than theyield stress of the hydraulically settable mixture is applied.

The yield stress and, hence, the form-stability of the extruded objectcan also be increased by either chemical additives (such as by adding arheology-modifying agent) or by adding energy to the system (such as byheating the extrusion apparatus or the extruded materials). For example,heating the material as it is extruded can activate a starch additive,thereby causing it to increase the yield stress of the extrudedmaterial. In addition, heat accelerates the hydration reaction betweenthe hydraulically settable binder and water, sometimes by factors ashigh as 10 or even 20 times the normal reaction rate. Indeed, it is thisdiscovery of how to manipulate the hydraulically settable compositionsin order to increase the form-stability of the compositions whileobtaining good flow during the formation process that make the presentinvention such a significant advancement in the art.

From the following discussion, it will be appreciated how each of thecomponent materials within the hydraulically settable mixture, as wellas the processing parameters, contributes to the primary designconstraints of the extrudable hydraulically settable mixtures so that awide variety of extruded articles can be produced therefrom. Specificcompositions are set forth in the examples given later in order todemonstrate how the maximization of the performance of each componentaccomplishes the combination of desired properties.

D. Hydraulically Settable Materials

The materials used to manufacture the extruded objects of the presentinvention develop strength through the chemical reaction of water and ahydraulically settable binder, such as hydraulic cement, calcium sulfate(or gypsum) hemihydrate (which is sometimes mixed with gypsum anhydride,commonly known as "anhydrite"), and other substances which harden afterbeing exposed to water. Even slag, blast furnace slag, fly ash, orsilica fume may be activated and act as a "hydraulically settablebinder."

The term "hydraulically settable materials" as used in thisspecification and the appended claims includes any material with astructural matrix and strength properties that are derived from ahardening or curing of a hydraulically settable binder. These includecementitious materials, plasters, and other hydraulically settablematerials as defined herein. The hydraulically settable binders used inthe present invention are to be distinguished from other cements orbinders such as polymerizable, water insoluble organic cements, glues,or adhesives.

The terms "hydraulically settable material," "hydraulic cementmaterials," or "cementitious materials," as used herein, are intended tobroadly define compositions and materials that contain both ahydraulically settable binder and water, regardless of the extent ofhydration or curing that has taken place. Hence, it is intended that theterm "hydraulically settable materials" shall include hydraulic paste orhydraulically settable mixtures in a green (i.e., unhardened) state, aswell as hardened hydraulically settable or concrete products. While in agreen state, hydraulically settable materials may also be referred to as"hydraulically settable mixtures."

1. Hydraulically Settable Binders

The terms "hydraulically settable binder" or "hydraulic binder," as usedin this specification and the appended claims, are intended to includeany inorganic binder (such as hydraulic cement, gypsum hemihydrate,calcium oxide, or mixtures thereof) which develops strength propertiesand hardness by chemically reacting with water and, in some cases, withcarbon dioxide in the air and water. The terms "hydraulic cement" or"cement" as used in this specification and the appended claims areintended to include cement clinker and crushed, ground, milled, andprocessed clinker in various stages of pulverization and in variousparticle sizes.

Examples of typical hydraulic cements known in the art include the broadfamily of portland cements (including ordinary portland cement withoutgypsum), MDF cement, DSP cement, Densit-type cements, Pyrament-typecements, calcium aluminate cements (including calcium aluminate cementswithout set regulators), plasters, silicate cements (includingβ-dicalcium silicates, tricalcium silicates, and mixtures thereof),gypsum cements, phosphate cements, high alumina cements, micro finecements, slag cements, magnesium oxychloride cements, and aggregatescoated with micro fine cement particles. The term "hydraulic cement" isalso intended to include other cements known in the art, such asα-dicalcium silicate, which can be made hydraulic under hydratingconditions within the scope of the present invention.

The basic chemical components of, e.g., portland cement include CaO,MgO, SiO₂, Al₂ O₃, Fe₂ O₃, SO₃, in various combinations and proportions.These react together in the presence of water in a series of complexreactions to form insoluble calcium silicate hydrates, carbonates (fromCO₂ in the air and added water), sulfates, and other salts or productsof calcium, magnesium, aluminum, and iron, together with hydratesthereof. These include tricalcium aluminate, dicalcium silicate,tricalcium silicate, and tetracalcium alumina ferrite. The aluminum andiron constituents are thought to be incorporated into elaboratecomplexes within the aforementioned materials. The cured cement productis a complex matrix of insoluble hydrates and salts which are complexedand linked together much like stone. This material is highly inert andhas both physical and chemical properties similar to those of naturalstone or dirt.

Gypsum is also a hydraulically settable binder that can be hydrated toform a hardened binding agent. One hydratable form of gypsum is calciumsulfate hemihydrate, commonly known as "gypsum hemihydrate." Thehydrated form of gypsum is calcium sulfate dihydrate, commonly known as"gypsum dihydrate." Calcium sulfate hemihydrate can also be mixed withcalcium sulfate anhydride, commonly known as "gypsum anhydrite" orsimply "anhydrite."

Although gypsum binders or other hydraulically settable binders such ascalcium oxide are generally not as strong as hydraulic cement, highstrength may not be as important as other characteristics (e.g., therate of hardening) in some applications. In terms of cost, gypsum andcalcium oxide have an advantage over hydraulic cement because they aresomewhat less expensive.

In addition, gypsum hemihydrate is known to set up or harden in a muchshorter time period than traditional cements. In fact, in use with thepresent invention, it will harden and attain most of its ultimatestrength within about thirty minutes. Hence, gypsum hemihydrate can beused alone or in combination with other hydraulically settable materialswithin the scope of the present invention. It has been found that addinggypsum hemihydrate to a hydraulically settable mixture containinghydraulic cement as a binder yields a mixture having a much lowerwater-to-cement ratio and, hence, higher strength according to theStrength Equation.

Terms such as "hydrated" or "cured" hydraulically settable mixture,material, or matrix refers to a level of substantial water-catalyzedreaction which is sufficient to produce a hydraulically settable producthaving a substantial amount of its potential or final maximum strength.Nevertheless, hydraulically settable materials may continue to hydratelong after they have attained significant hardness and a substantialamount of their final maximum strength.

Terms such as "green" or "green state" are used in conjunction withhydraulically settable mixtures which have not achieved a substantialamount of their final strength, regardless of whether such strength isderived from artificial drying, curing, or other means. Hydraulicallysettable mixtures are said to be "green" or in a "green state" justprior and subsequent to being molded into the desired shape. The momentwhen a hydraulically settable mixture is no longer "green" or in a"green state" is not necessarily a clear-cut line of demarcation, sincesuch mixtures generally attain a substantial amount of their totalstrength only gradually over time. Hydraulically settable mixtures can,of course, show an increase in "green strength" and yet still be"green." For this reason, the discussion herein often refers to theform-stability of the hydraulically settable material in the greenstate.

As mentioned above, preferred hydraulically settable binders includeportland white cement, portland grey cement, micro fine cement, highalumina cement, slag cement, gypsum hemihydrate, and calcium oxide,mainly because of their low cost and suitability for the manufacturingprocesses of the present invention. This list of cements is by no meansexhaustive, nor in any way is it intended to limit the types of binderswhich would be useful in making the hydraulically settable containerswithin the scope of the claims appended hereto. It has been found thatportland grey cement improves the cohesive nature of the greenhydraulically settable mixture better than other types of cements.

The present invention may include other types of cementitiouscompositions such as those discussed in copending (now abandoned) U.S.patent application Ser. No. 07/981,615, filed Nov. 25, 1992 in the namesof Hamlin M. Jennings, Ph.D., Per Just Andersen, Ph.D. and Simon K.Hodson, and entitled "Methods of Manufacture And Use For HydraulicallyBonded Cement," which is a continuation-in-part of U.S. patentapplication Ser. No. 07/856,257, filed Mar. 25, 1992 in the names ofHamlin M. Jennings, Ph.D. and Simon K. Hodson, and entitled"Hydraulically Bonded Cement Compositions and Their Methods ofManufacture and Use" (now abandoned), which was a file wrappercontinuation of U.S. patent application Ser. No. 07/526,231 (alsoabandoned). In these applications, powdered hydraulic cement is placedin a near net final position and compacted prior to the addition ofwater for hydration. For purposes of disclosing the use of suchcompositions, the forgoing patents applications are incorporated hereinby specific reference.

Additional types of hydraulic cement compositions include those whereincarbon dioxide is mixed with hydraulic cement and water. Hydrauliccement compositions made by this method are known for their ability tomore rapidly achieve high green strength. This type of hydraulic cementcomposition is discussed in copending U.S. patent application Ser. No.07/418,027 filed Oct. 10, 1989, in the names of Hamlin M. Jennings,Ph.D. and Simon K. Hodson, and entitled "Process for Producing ImprovedBuilding Material and Products Thereof," now U.S. Pat. No. 5,232,496,wherein water and hydraulic cement are mixed in the presence of acarbonate source selected from the group consisting of carbon dioxide,carbon monoxide, carbonate salts, and mixtures thereof. For purposes ofdisclosure, the forgoing patent is incorporated herein by specificreference.

2. Hydraulic Paste

In each embodiment of the present invention, the hydraulic paste(including cement paste) is the key constituent which eventually givesthe extruded object the ability to set up and develop strengthproperties. The term "hydraulic paste" shall refer to a hydraulicallysettable binder which has been mixed with water. More specifically, theterm "cement paste" shall refer to hydraulic cement which has been mixedwith water. The terms "hydraulically settable," "hydraulic," or"cementitious" mixture shall refer to a hydraulic cement paste to whichaggregates, fibers, rheology-modifying agents, dispersants, or othermaterials have been added, whether in the green state or after it hashardened and/or cured. The other ingredients added to the hydraulicpaste serve the purpose of altering the properties of the unhardened, aswell as the final hardened product, including, but not limited to,tensile strength, compressive strength, shrinkage, flexibility, bulkdensity, color, porosity, surface finish, and texture.

Although the hydraulically settable binder is understood to be thecomponent which allows the hydraulically settable mixture to set up, toharden, and to achieve much of the strength properties of the material,certain hydraulically settable binders also aid in the development ofbetter early cohesion and green strength. For example, hydraulic cementparticles are known to undergo early gelating reactions with water evenbefore it becomes hard; this can contribute to the internal cohesion ofthe mixture.

It is believed that aluminates, such as those more prevalent in portlandgrey cement (in the form of tricalcium aluminates and tetracalciumalumina ferrites) are responsible for a colloidal interaction betweenthe cement particles during the earlier stages of hydration. This inturn causes a level of flocculation/gelation to occur between the cementparticles. The gelating, colloidal, and flocculating affects of suchbinders has been shown to increase the moldability (i.e., plasticity) ofhydraulically settable mixtures made therefrom.

The percentage of hydraulically settable binder within the overallmixture varies depending on the identity of the other addedconstituents. However, the hydraulically settable binder is preferablyadded in an amount ranging from between about 1% to about 90% as apercentage by weight of the wet hydraulically settable mixture, morepreferably within the range from between about 8% to about 60%, and mostpreferably from about 10% to about 45%. From the disclosure and examplesset forth herein, it will be understood that this wide range of weightpercentages covers the many different types of articles that may beformed by extruding a hydraulically settable mixture.

Despite the foregoing, it will be appreciated that all concentrationsand amounts are critically dependent upon the qualities andcharacteristics that are desired in the final product. For example, in avery thin-walled structure (even as thin as 0.05 mm) where high strengthis needed, such as in an extruded drinking straw, it may be moreeconomical to have a very high percentage of hydraulically settablebinder with little or no aggregate. In such a case, it may be desirableto include a high amount of fiber to impart flexibility and toughness.

The other important constituent of hydraulic paste is water. Bydefinition, water is an essential component of the hydraulicallysettable materials within the scope of the present invention. Thehydration reaction between hydraulically settable binder and wateryields reaction products which give the hydraulically settable materialsthe ability to set up and develop strength properties.

In most applications of the present invention, it is important that thewater to hydraulically settable binder ratio be carefully controlled inorder to obtain a hydraulically settable mixture which after extrusionis self-supporting in the green state. Nevertheless, the amount of waterto be used is dependent upon a variety of factors, including the typesand amounts of hydraulically settable binder, aggregates, fibrousmaterials, rheology-modifying agents, and other materials or additiveswithin the hydraulically settable mixture, as well as the extrusionconditions to be used, the specific article to be extruded, and itsproperties.

The preferred amount of added water within any given application isprimarily dependent upon two key variables: (1) the amount of waterwhich is required to react with and hydrate the binder; and (2) theamount of water required to give the hydraulically settable mixture thenecessary rheological properties and workability.

In order for the green hydraulically settable mixture to have adequateworkability, water must generally be included in quantities sufficientto wet each of the particular components and also to at least partiallyfill the interstices or voids between the particles (including, e.g.,binder particles, aggregates, and fibrous materials). If water solubleadditives are included, enough water must be added to dissolve orotherwise react with the additive. In some cases, such as where adispersant is added, workability can be increased while using lesswater.

The amount of water must be carefully balanced so that the hydraulicallysettable mixture is sufficiently workable, while at the same timerecognizing that lowering the water content increases both the greenstrength and the final strength of the hardened, extruded product. Theappropriate rheology to meet these needs can be defined in terms ofyield stress. In order for the hydraulically settable mixtures to haveadequate green strength and form-stability upon being extruded into thedesired article, the hydraulically settable mixture will preferably havea yield stress greater than or equal to about 2 kPa, more preferablygreater than or equal to about 10 kPa, and most preferably greater thanor equal to about 100 kPa. It should be understood that these figuresrepresent preferred minima. There is no limit to the yield stress which,depending on a number of factors such as the water deficiency, themorphology of the particles, the amount of rheology-modifying agentwithin the mixture, may be much higher. The desired level of yieldstress can be (and may necessarily have to be) adjusted depending on theparticular shape or article to be extruded.

Because the hydraulically settable mixtures of the present inventionexhibit shear thinning, there is no single preferred viscosity, althoughthe mixtures should have a viscosity adequate to make them form-stablebut small enough to render them flowable using an extruder. In general,however, the apparent viscosity will usually be about 10⁷ poise orgreater at a shear rate of 0 s⁻¹, about 10⁴ poise or greater at a shearrate of 20 s⁻, and about 2×10² poise or greater at a shear rate of 1000s⁻¹.

One skilled in the art will understand that when more aggregates orother water absorbing additives are included, a higher water tohydraulically settable binder ratio is necessary in order to provide thesame level of workability and available water to hydrate thehydraulically settable binder. This is because a greater aggregateconcentration provides a greater volume of interparticulate intersticesor voids which must be filled by the water as a fraction of thehydraulically settable binder volume. Porous aggregates can alsointernally absorb significant mounts of water due to their high voidcontent. Based on the foregoing qualifications, typically hydraulicallysettable mixtures within the scope of the present invention will have awater to hydraulically settable binder ratio within a range from about0.05 to about 4, preferably about 0.1 to about 1, and most preferablyfrom about 0.15 to about 0.5.

Because of the higher levels of particle packing density of thehydraulically settable binder particles within a typical mixture of thepresent invention, the specific gravity of the hydraulic paste fractionof the hydraulically settable mixture will preferably (in cases wherehigher strength is desired) be greater than about 2.2, more preferablygreater than about 2.5, and most preferably greater than about 2.6.

It should be understood that the hydraulically settable binder has aninternal drying effect on the hydraulically settable mixture because thebinder particles chemically react with water and reduce the mount offree water within the interparticulate interstices. This internal dryingeffect can be enhanced by including faster reacting hydraulicallysettable binders, such as gypsum hemihydrate, along with slower reactinghydraulic cement.

3. Water Deficiency

In many cases, the amount of water needed to both hydrate the binder andalso impart the desired rheology to the hydraulically settable mixturemay be more accurately described in terms of either volume percent or"water deficiency." The level of water deficiency is determined bysubtracting the volume of free interstitial water from the totalinterstitial space, and then dividing the result by the totalinterstitial space.

    water deficiency=(V.sub.space -V.sub.water)/V.sub.space

By way of example, and in order to better illustrate the concept ofwater deficiency, the hydraulically settable mixture can contain addedwater and yet be 100% water deficient (i.e., have no interstitial water)in the case where all of the water has either been absorbed into thepores of the aggregates or reacted with the hydraulically settablebinder.

Of course, it should be understood that the amount of water that hasactually reacted with the hydraulically settable binder at any giventime after the hydraulically settable binder and water have been mixedtogether will usually be significantly lower than the calculatedstoichiometric equivalent of water needed to substantially hydrate thebinder. Because of the kinetics of the hydration reaction, the waterdoes not immediately react completely with the hydraulically settablebinder, but only over time and generally during the curing stage afterthe material has been extruded.

Hence, water within the theoretical stoichiometric equivalent amountwhich does not react with the binder is generally available to fill theinterstices or voids between the particles (if not absorbed by theaggregate material). Water that has not chemically reacted with thehydraulically settable binder may be classified as either gel water orcapillary water. Both forms tend to decrease the strength of the finalcured material and, hence, should be minimized where possible. Becausethe amount of water available to fill the interstices directly affectsthe workability and rheology of the hydraulically settable mixture, itwill usually be necessary to determine the amount of unboundstoichiometric water available to fill the interstices and lubricate theparticles at any given time after mixing, although initially almost allof the added water is free because of the slowness of the hydrationreaction.

Some of the factors that will determine what percentage of thecalculated stoichiometric equivalent of water will have actually reactedwith the hydraulically settable binder, include the reactivity (or rateof reaction) of the binder, the temperature of the mixture, the particlesize of the binder, the level of mixing, the wettability of thecomponents within the overall mixture, and the time which has elapsedsince the addition of water.

For example, hydraulically settable binders having a high rate ofreaction will absorb or react with the available water more quickly thanbinders having lower rates of reaction. As with most reactions, highertemperatures generally will increase the rate of reaction of allhydraulically settable binders, and hence, the rate of water removal ofthe binder.

Moreover, hydraulically settable binders with smaller particle sizeswill also tend to react with more water because they will have a greateroverall surface area that will come in contact and react with theavailable water. Of course, the tendency of the hydraulically settablebinder particles to react with water is dependent upon the level ofmixing. More thoroughly blended mixtures will result in greater contactbetween water and binder particles, and, hence, greater reaction withthe water.

The extent of any reaction that has not reached equilibrium is alsodependent upon the time which has elapsed since the reactants have beenmixed together. Obviously, a hydraulically settable mixture in which thehydraulically settable binder has been in contact with water over agreater period of time will show a greater level of reaction between thewater and the binder. Nevertheless, where a dispersant has been added,longer mixing time increases the specific surface area for adsorption ofthe dispersant, thereby creating a more fluid mixture in the short run.In general, substantial setting of hydraulic cement usually occurswithin about 5 hours.

Aside from the dynamics of the reaction between the hydraulicallysettable binder and water, the other components within the hydraulicallysettable mixture will also affect to some degree the absorption by orreaction of the water with the binder particles. Certain additives, suchas water soluble rheology-modifying agents, will compete with the binderparticles and actually absorb some of the available water.

In addition, other additives such as dispersants can impede the reactionbetween water and hydraulically settable binder particles. Whether agiven component or reaction condition will increase or decrease thereaction between the water and the hydraulically settable binderparticles must be carefully determined while designing any particularmix design. However, one skilled in the art will be able to predict theeffect of a given component or reaction condition on the tendency of thewater to react with the hydraulically settable binder, at least on thebasis of empirical observation.

Once it has been determined how much water will actually react with thecement, the next step is to determine how much "interstitial water"should be added in addition to this reacted or absorbed amount.Interstitial water is the water which is available to fill the voids orinterstices and which will directly affect the workability of thehydraulically settable mixture. The preferred amount of interstitialwater that will be required is determined by a combination of factors,including the particle packing density of the mixture, thecompressibility of the mixture, and the pressure exerted on the mixtureby the extruder.

Knowing the particle packing density allows one to determine the volumeof interstitial space within the uncompressed mixture which willinitially be filled by interstitial water. Knowing the compressibilityof the mixture and the pressure that will be exerted allows one todetermine the expected reduction of interstitial space when thehydraulically settable mixture is subjected to a given pressure duringthe extrusion process.

Where the particle packing density is lower, there will be moreinterstitial space as a percentage of the overall volume of the mixture,and more water will be required to fill this space. Conversely, wherethe particle packing density is greater, there will be less interstitialspace as a percentage of the overall volume of the mixture, and lesswater will be required to fill this space. How to optimize the packingdensity will be discussed hereinafter.

Similarly, where the hydraulically settable mixture will be subjected toa greater amount of pressure during the extrusion process, thecompression step will more dramatically reduce the volume ofinterstitial space, which in turn means that less interstitial waterwill be required initially in order to achieve the desired rheology.Also, including less water (higher deficiency) allows the particles tobe brought into more intimate contact during the compression process,resulting in a final cured product having less porosity, higher densityand greater strength.

Conversely, where the hydraulically settable mixture will be subjectedto a lesser amount of pressure during the extrusion process, thecompression step will less dramatically reduce the volume ofinterstitial space, which in turn means that more interstitial waterwill be required initially in order to achieve the desired rheology.Certain aggregates, such as sand, have relatively low compressibility.(How much pressure that may be exerted on the hydraulically settablemixture without destroying the integrity of the aggregate particlestherein depends on the compressive strength of the aggregate particles.)

The key is to add just enough water in order to substantially occupy theinterstitial space when the mixture is compressed during the extrusionprocess. Adding more water than what is required to fill the intersticesduring the compression of the extruded mixture would reduce both thegreen strength of the extruded product as well as the final strength ofthe cured material (according to the Strength Equation).

In light of the foregoing, it has been found that adequate workabilityof a hydraulically settable mixture that will be subjected to increasedpressure can be obtained when a deficiency of water is included. Theamount of water may be expressed in terms of volume percent, and, ifdeficient, will be less than the volume of the interstitial space, whichis determined by subtracting the natural packing density from 1. Forexample, if the natural packing density is 65%, the mixture will bedeficient in water if the water is included in an amount of less thanabout 35% by volume of the mixture. The amount of water that is requiredto create adequate workability will depend somewhat on the relativequantities of the mixture components, such as the hydraulically settablebinder particles, aggregates, and fibers. Nevertheless, it is generallynot the identity or relative quantities of the components but theoverall volume and packing density of the components that will determinehow much water should be added to achieve a hydraulically settablemixture having the desired rheological and plastic-like properties.

The amount of added water may, therefore, be expressed in terms of"water deficiency" before the mixture is compressed during the extrusionprocess. In mixtures relying upon the principles of particle packing andwater deficiency in order to attain the desired rheology, the level ofwater deficiency will be within the broad range from between about 1% toabout 90%. Because the preferred level of water deficiency is highlydependent upon many other variables, such as the components of thehydraulically settable mixture, the rheology of the mixture, and thelevel of particle packing efficiency, as well as the desired propertiesof the extruded product, there is no more narrow preferred range ofwater deficiency. Where a high level of rheology-modifying agent isemployed, it may be possible to extrude a mixture having excess water(or "negative" water deficiency).

Nevertheless, for any given mixture it will usually be preferable toinclude the minimum quantity of water necessary to allow it to flowunder the desired extrusion pressure and have enough internal cohesionto hold together once an article has been extruded from the mixture. Theminimum amount of water necessary for the hydraulically settable mixtureto flow may further be reduced by the addition of admixtures, such asplasticizers or dispersants, as set forth more fully herein. Where verylow levels of water are employed, it may be necessary in some cases topelletize the hydraulically settable mixture in order to increase theextrudability of the mixture.

Nevertheless, as a general rule, a mixture having a greater waterdeficiency will generally be stiffer and have lower workabilityinitially. Conversely, a mixture having a lower water deficiency willgenerally have lower viscosity and greater workability initially. Thelevel of stiffness, viscosity, or workability that will be desired forany given mixture will depend upon the extrusion process of a givensituation. Of course, during the extrusion process when thehydraulically settable mixture is compressed, the level of waterdeficiency will decrease, often dramatically. In some cases it mayapproach or even exceed 0%. (A negative water deficiency means thatthere is a surplus or excess of water; that is, the volume of waterexceeds the volume of interstitial voids between the solid particlesafter they have been compacted during the extrusion process.)

Nevertheless, hydraulically settable mixtures having a higher particlepacking density will generally be able to contain a greater deficiencyof water and yet be highly extrudable under pressure, as compared tomixtures which have a lower particle packing density. For example, whilethe particle packing density of a hydraulically settable mixture havinga natural packing density of 50% might increase to 65%, one with apacking density of 80% might increase to 95%. The drop in interstitialspace in the former case (50% to 35%) is slight compared to in thelatter (20% to 5%), which is a four-fold decrease. Hence, the mixturewith the higher particle packing density will experience a much moredramatic drop in the apparent water deficiency.

In some cases, it may also be preferable to add "excess water" or morewater than is needed to fill the interstitial space in order to decreasethe viscosity and increase the workability of the mixture. However, inorder to obtain immediate green strength, it may be necessary in thosecases to heat the surface the of extruded article using a heated die inorder to remove some or all of the "excess water." In addition, gypsumhemihydrate may be added to react with some or all of the excess waterand thereby increase the form stability of the extruded article.

In the case where more water or dispersant is added initially in orderto give the hydraulically settable mixture greater workability,increased form-stability of the extruded object or shape can be obtainedby, for example, immediately passing the object through a heating tunnelor vacuum chamber. This causes part of the water to be driven off in theform of vapor or steam from the article surface, which reduces thevolume of interstitial water, increases the friction between theparticles, and result in a quick increase in form-stability. However,overheating the extruded article, or drying it out too quickly, may harmthe micro structure of the article, thereby reducing the strength of thearticle.

E. Rheology-modifying Agents

The inclusion of a rheology-modifying agent acts to increase the plasticor cohesive nature of the hydraulically settable mixture so that itbehaves more like a moldable or extrudable clay. The rheology-modifyingagent tends to thicken the hydraulically settable mixture by increasingthe yield stress of the mixture without greatly increasing the viscosityof the mixture. Raising the yield stress in relation to the viscositymakes the material more plastic-like (or clay-like) and moldable, whilegreatly increasing the subsequent form-stability or green strength.

A variety of natural and synthetic organic rheology-modifying agents maybe used which have a wide range of properties, including high or lowviscosity, yield stress, and solubility in water. Although many of therheology-modifying agents contemplated by the present invention might bevery soluble in water, the insoluble reaction products of hydrauliccement and water encapsulate the rheology-modifying agent and prevent itfrom dissolving out of an extruded hydraulically settable article thatis exposed to water.

The various rheology-modifying agents contemplated by the presentinvention can be roughly organized into the following categories: (1)polysaccharides and derivatives thereof, (2) proteins and derivativesthereof, and (3) synthetic organic materials. Polysacchariderheology-modifying agents can be further subdivided into (a)cellulose-based materials and derivatives thereof, (b) starch basedmaterials and derivatives thereof, and (c) other polysaccharides.

Suitable cellulose-based rheology-modifying agents include, for example,methylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxyethylpropylcellulose, etc. The entirerange of possible permutations is enormous and cannot be listed here,but other cellulose materials which have the same or similar propertiesas these would also work well.

Suitable starch based materials include, for example, amylopectin,amylose, seagel, starch acetates, starch hydroxyethyl ethers, ionicstarches, long-chain alkylstarches, dextrins, amine starches, phosphatestarches, and dialdehyde starches.

Other natural polysaccharide based rheology-modifying agents include,for example, alginic acid, phycocolloids, agar, gum arabic, guar gum,locust bean gum, gum karaya, and gum tragacanth.

Suitable protein-based rheologyomodifying agents include, for example,Zein® (a prolamine derived from corn), collagen derivatives extractedfrom animal connective tissue such as gelatin and glue, and casein (theprincipal protein in cow's milk).

Finally, suitable synthetic organic plasticizers include, for example,polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol,polyvinylmethyl ether, polyacrylic acids, polyacrylic acid salts,polyvinylacrylic acids, polyvinylacrylic acid salts, polyacrylimides,ethylene oxide polymers, polylactic acid, synthetic clay, and latex,which may be a styrene-butadiene copolymer. The rheology of polylacticacid is significantly modified by heat and could be used alone or incombination with any other of the foregoing rheology-modifying agents.

A currently preferred rheology-modifying agent ismethylhydroxyethylcellulose, examples of which are Tylose® FL 15002 andTylose® 4000, both of which are available from HoechstAktiengesellschaft of Frankfurt, Germany. Lower molecular weightrheology-modifying agents such as Tylose® 4000 generally act toplasticize or lubricate the mixture rather than thicken it, which aidsin flowability during the extrusion procedure.

More particularly, lower molecular weight rheology-modifying agentsimprove the extrusion process by lubricating the particles. This reducesthe friction between the particles as well as between the mixture andthe adjacent extruder surfaces. Although a methylhydroxyethylcelluloserheology-modifying agent is preferred, almost any non-toxicrheology-modifying agent (including any listed above) which imparts thedesired properties would be appropriate.

Another preferred rheology-modifying agent that can be used instead of,or in conjunction with, Tylose® is polyethylene glycol having amolecular weight of between 20,000 and 35,000. Polyethylene glycol worksmore as a lubricant and adds a smoother consistency to the mixture. Forthis reason, polyethylene glycol might be referred more precisely as a"plasticizer." In addition, it gives the extruded hydraulically settablematerial a smoother surface. Stearates can also be added to lubricatethe hydraulically settable mixture.

Finally, starch-based rheology-modifying agents are of particularinterest within the scope of the present invention because of theircomparatively low cost compared to cellulose-based rheology-modifyingagents such as Tylose®. Although starches typically require heat and/orpressure in order to gelate, starches may by modified and prereacted sothat they can gel at room temperature. The fact that starches, as wellas many of the other rheology-modifying agents listed above, have avariety of solubilities, viscosities, and rheologies allows for thecareful tailoring of the desired properties of a mix design so that itwill conform to the particular manufacturing and performance criteria ofthe desired extruded article.

The rheology-modifying agents within the hydraulically settablematerials of the present invention are preferably included in a rangefrom about 0.1% to about 5% by weight of the hydraulically settablemixture exclusive of water, more preferably in a range from about 0.25%to about 2%, and most preferably in a range from about 0.5% to about 1%.The actual amount to be used will depend upon the nature of the extrudedarticle or product.

F. Aggregates

Aggregates common in the concrete industry may be used in thehydraulically settable mixtures of the present invention. In the casewhere relatively thin-walled articles will be extruded, and in order forthe mixtures to remain extrudable through the reduced cross-sectiondies, the diameter of the aggregates used will most often be less thanabout 25% of the smallest cross-section of the structural matrix of theextruded article.

Aggregates may be added to increase the compressive strength, decreasethe cost by acting as a filler, and affect the particle packing densityof the resultant hydraulically settable materials. Aggregates are alsouseful for creating a smooth surface finish, particularly plate-likeaggregates. The tensile and compressive strengths of the aggregate willoften affect the tensile and compressive strengths of the final hardenedproduct.

Examples of useful aggregates include sand, dolomite, gravel, rock,basalt, granite, limestone, sandstone, glass beads, aerogels, xerogels,seagel, mica, clay, synthetic clay, alumina, silica, fly ash, silicafume, tabular alumina, kaolin, glass microspheres, ceramic spheres,gypsum dihydrate, calcium carbonate, calcium aluminate, xonotlite (acrystalline calcium silicate gel), unreacted cement particles, and othergeologic materials. Both hydrated and unhydrated cement particles mayalso be considered to be "aggregates" in the broadest sense of the term,depending on their distribution and the nature of their incorporationwithin the hydraulically settable matrix. Even discarded hydraulicallysettable materials, such as discarded sheets, containers, boards, orother objects of the present invention can be employed as aggregatefillers and strengtheners. Silica fume and fly ash also can be added toreduce the porosity of the hydraulically settable mixture and increaseits workability and cohesiveness.

The amount of the aggregate will vary depending upon the particularapplication or purpose, and can vary greatly from no added aggregate upto about 90% by weight of the green hydraulically settable mixture, morepreferably within the range from between about 3% to about 70% byweight, and most preferably from between about 20% to about 50% byweight.

Both clay and gypsum are particularly important aggregate materialsbecause of their ready availability, extreme low cost, workability, andease of formation. Gypsum hemihydrate can also provide a degree ofbinding and strength if added in high enough amounts. Clay is a generalterm used to identify all earths that form a paste with water and hardenwhen dried. The predominant clays include silica and alumina (used formaking pottery, tiles, brick, and pipes) and kaolinite. The twokaolinitic clays are anauxite, which has the chemical formula Al₂ O₃·3SiO₂ ·2H₂ O, and montmorillonite, which has the chemical formula Al₂O₃ ·4SiO₂ ·H₂ O. However, clays may contain a wide variety of othersubstances such as iron oxide, titanium oxide, calcium oxide, zirconiumoxide, and pyrite.

In addition, although clays have been used for millennia and can obtainhardness even without being fired, such unfired clays are vulnerable towater degradation and exposure, are extremely brittle, and have lowstrength. Nevertheless, clay makes a good, inexpensive aggregate withinthe hydraulically settable structural matrix.

Similarly, gypsum hemihydrate is also hydratable and forms the dihydrateof calcium sulfate in the presence of water. Thus, gypsum may exhibitthe characteristics of both an aggregate and a binder depending onwhether (and in what proportion) the hemihydrate or dihydrate form isadded to the hydraulically settable mixture.

It is often preferable, according to the present invention, to include aplurality of differently sized and graded aggregates capable of morecompletely filling the interstices between the aggregate andhydraulically settable binder particles. Optimizing the particle packingdensity reduces the amount of water necessary to obtain adequateworkability by eliminating spaces which would otherwise be filled withinterstitial water, often referred to as "capillary water." In addition,using less water increases the strength of the final hardened product(according to the Strength Equation).

In order to optimize the packing density, differently sized aggregateswith particle sizes ranging from as small as about 0.01 microns to aslarge as about 4 mm may be used. (Of course, the desired purpose andthickness of the resulting product will dictate the appropriate particlesizes of the various aggregates to be used.)

In certain preferred embodiments of the present invention, it may bedesirable to maximize the amount of the aggregates within thehydraulically settable mixture in order to maximize the properties andcharacteristics of the aggregates (such as qualities of strength, lowdensity, or high insulation). The use of particle packing techniques maybe employed within the hydraulically settable material in order tomaximize the amount of the aggregates.

A detailed discussion of particle packing can be found in the followingarticle coauthored by one of the inventors of the present invention:Johansen, V. & Andersen, P. J., "Particle Packing and ConcreteProperties," Materials Science of Concrete II at 111-147, The AmericanCeramic Society (1991). Further information is available in the DoctoralDissertation of Andersen, P. J. "Control and Monitoring of ConcreteProduction--A Study of Particle Packing and Rheology," The DanishAcademy of Technical Sciences. For purposes of teaching particle packingtechniques, the disclosures of the foregoing article and thesis areincorporated herein by specific reference.

A detailed description of how to select a mixture of aggregates andaggregate particle sizes to accommodate a given mix design criteria canbe found within co-pending (now abandoned) U.S. patent application Ser.No. 08/109,100, filed Aug. 18, 1993, in the names of Per Just Andersen,Ph.D. and Simon K. Hodson "Design Optimized Compositions And ProcessesFor Microstructurally Engineering Cementitious Mixtures." For purposesof disclosure, this reference is incorporated herein by specificreference.

G. Fibers

As used in the specifications and appended claims, the terms "fibers"and "fibrous materials" include both inorganic fibers and organicfibers. Fibers are a particular kind of aggregate which may be added tothe hydraulically settable mixture to increase the cohesion, elongationability, deflection ability, toughness, fracture energy, and flexural,tensile, and even compressive strengths. Fibrous materials reduce thelikelihood that the extruded hydraulically settable object will shatterwhen a strong cross-sectional force is applied.

Fibers which may be incorporated into the structural matrix arepreferably naturally occurring fibers, such as cellulosic fibersextracted from hemp, cotton, sisal, plant leaves, wood or stems, orfibers made from glass, silica, ceramic, or metal. Glass fibers arepreferably pretreated to be alkali resistant.

Preferred fibers of choice include glass fibers, abaca, bagasse, woodfibers (both hardwood or softwood, such as southern hardwood or southernpine), ceramic fibers (such as alumina, silica nitride, silica carbide,and graphite,) and cotton. Recycled paper fibers can be used, but theyare somewhat less desirable because of the fiber degradation that occursduring the original paper manufacturing process, as well as in therecycling process. Any equivalent fiber, however, which imparts strengthand flexibility is also within the scope of the present invention. Abacafibers are available from Isarog Inc. in the Philippines. Glass fibers,such as Cemfill®, are available from Pilkington Corp. in England.

The fibers used to make the hydraulically settable materials of thepresent invention preferably have a high length to width ratio (or"aspect ratio") because longer, narrower fibers can impart more strengthto the matrix without significantly adding bulk and mass to the mixture.The fibers should have an aspect ratio of at least about 10:1,preferably at least about 100:1, and most preferably at least about200:1. However, although the toughness and tensile strength of the finalproduct are increased as the aspect ratio of the fibers is increased,fibers with lower aspect ratios are cheaper, provide better particlepacking, and are easier to disperse within the hydraulically settablemixture.

The amount of fibers added to the hydraulically settable matrix willvary depending upon the desired properties of the final product, withstrength, toughness, flexibility, and cost being the principal criteriafor determining the amount of fiber to be added in any mix design. Inmost cases, fibers will be added in an amount within a range from about0.5% to about 30% by volume of the green hydraulically settable mixture,more preferably within the range from about 1% to about 20% by volume,and most preferably within the range from about 2% to about 10% byvolume. The extrusion process tends to longitudinally orient the fibersand results in a tougher product.

It will be appreciated, however, that the strength of the fiber is avery important feature in determining the amount of the fiber to beused. The stronger the tensile strength of the fiber, the less theamount that must be used to obtain the same level of tensile strength inthe resulting product. Of course, while some fibers have a high tensilestrength, other types of fibers with a lower tensile strength may bemore elastic. Hence, a combination of two or more fibers may bedesirable in order to obtain a resulting product that maximizes multiplecharacteristics, such as high tensile strength and high elasticity.

In addition, while ceramic fibers are generally far more expensive thannaturally occurring or glass fibers, their use will nevertheless beeconomical in some cases due to their far superior tensile strengthproperties. Obviously the use of more expensive fibers becomes moreeconomical as the cost restraints of the extruded object are relaxed,such as where a comparable object made from a competing material isrelatively expensive.

It should be understood that the fibers used within the scope of thepresent invention differ from fibers typically employed in making paperor paperboard objects, primarily in the way in which the fibers areprocessed. In the manufacture of paper, either a Kraft or a sulphiteprocess is typically used to form the pulp sheet. In the Kraft process,the pulp fibers are "cooked" in a NaOH process to break up the fibers.In a sulphite process, acid is used in the fiber disintegration process.Both processes greatly reduce the strength of the resulting fibers, andfibers made by these processes are not preferred in most cases.Consequently, far less fiber may be added to the hydraulically settablemixtures of the present invention while still deriving a high level ofstrength from the fibers.

It should also be understood that some fibers, such as southern pine andabaca, have high tear and burst strengths, while others, such as cotton,have lower strength but greater flexibility. In the case where bothflexibility and high tear and burst strength is desired, a mixture offibers having the various properties can be added to the mixture.

H. Dispersants

The term "dispersant" is used hereinafter to refer to the class ofmaterials which can be added to reduce the amount of water that must beadded in order to maintain the same flow properties. Dispersantsgenerally work by reducing the viscosity and yield stress of thehydraulically settable mixture. A more detailed description of the useof dispersants may be found in the Master's Thesis of Andersen, P. J.,"Effects of Organic Superplasticizing Admixtures and Their Components onZeta Potential and Related Properties of Cement Materials" (1987). Forpurposes of disclosure, the above-referenced article is incorporatedherein by specific reference.

Dispersants generally work by being adsorbed onto the surface of thehydraulically settable binder particles and/or into the near colloiddouble layer of the binder particles. This creates a negative chargearound the surfaces of particles, causing them to repel each other. Thisrepulsion of the particles adds "lubrication" by reducing the "friction"or attractive forces that would otherwise cause the particles to havegreater interaction. Because of this, less water can be added initiallywhile maintaining the workability of the hydraulically settable mixture.

Greatly reducing the viscosity and yield stress may be desirable whereclay-like properties, cohesiveness, and/or form-stability are lessimportant or where it is desired to use less water initially. Adding adispersant aids in keeping the hydraulically settable mixture workableeven when very little water is added, particularly where there is a"deficiency" of water. Hence, adding a dispersant allows for an evengreater deficiency of water, although the extruded article may havesomewhat less form-stability if too much dispersant is used.Nevertheless, including less water initially will theoretically yield astronger final cured article, according to the Strength Equation.

Whether or not there is a deficiency of water is both a function of thestoichiometric amount of water required to hydrate the binder and theamount of water needed to occupy the interstices between the particlesin the hydraulically settable mixture, including the hydraulicallybinder particles themselves and the particles within the aggregatematerial and/or fibrous material. As stated above, improved particlepacking reduces the volume of the interstices between the hydraulicallysettable binder and aggregate particles and, hence, the amount of waternecessary to fully hydrate the binder and maintain the workability ofthe hydraulically settable mixture by filling the interstitial space.

However, due to the nature of the coating mechanism of the dispersant,the order in which the dispersant is added to the mixture is oftencritical. If a flocculating/gelating agent such as Tylose® or starch isadded, the dispersant must be added first and the flocculating agentsecond. Otherwise, it will be more difficult for the dispersant tobecome adsorbed on the surface of the hydraulically settable binderparticles as the Tylose® or starch may become irreversibly adsorbed ontothe surface of the particles, thereby bridging them together rather thancausing them to repel each other.

A preferred dispersant is sulfonated naphthalene-formaldehydecondensate, an example of which is WRDA 19, which is available from W.R.Grace, Inc. located in Baltimore. Other dispersants which would workwell include sulfonated melamineformaldehyde condensate, lignosulfonate,and acrylic acid. The sodium salt of sulfonated naphthalene-formaldehydecondensate can be added after the hydraulic cement and water have hadsufficient time to form early hydration products (such as ettringite) inorder to increase the specific surface area of the cement particles,which allows for greater dispersion of the particles.

Another way to improve the flowability of the hydraulically settablemixture under lower pressure is by adding other reactive products havinga high specific surface area, such as silica fume. This also increasesthe yield stress and, hence, the form-stability of the extruded article.

The amount of added dispersant will generally range up to about 5% byweight of the hydraulically settable binder, more preferably within therange of between about 0.25% to about 4%, and most preferably within therange of between about 0.5% to about 2%. However, it is important not toinclude too much dispersant as it tends to retard the hydrationreactions between, e.g., hydraulic cement and water. Adding too muchdispersant can, in fact, prevent hydration, thereby destroying thebinding ability of the hydraulic paste altogether.

The dispersants contemplated within the present invention have sometimesbeen referred to in the concrete industry as "superplasticizers," "waterreducers," or "high range water reducers." In order to betterdistinguish dispersants from rheology-modifying agents, which often actas plasticizers, the term "superplasticizer" will not be used in thisspecification.

I. Set Accelerators

In some cases, it may be desirable to accelerate the initial set of thehydraulically settable mixture and obtain earlier form stability of theextruded article by adding to the mixture an appropriate setaccelerator. These include Na₂ CO₃, KCO₃, KOH, NaOH, CaCl₂, CO₂,triethanolamine, aluminates, and the inorganic alkali salts of strongacids, such as HCl, HNO₃, and H₂ SO₄. In fact, any compound whichincreases the solubility of gypsum and Ca(OH)₂ will tend to acceleratethe initial set of hydraulically settable mixtures, particularlycementitious mixtures.

The amount of set accelerator which may be added to a particularhydraulically settable mixture will depend upon the degree of setacceleration that is desired. This in turn will depend on a variety offactors, including the mix design, the time interval between the stepsof mixing the components and molding or extruding the hydraulicallysettable mixture, the temperature of the mixture, and the identity ofthe set accelerator. One of ordinary skill in the art will be able toadjust the amount of added set accelerator according to the parametersof a particular manufacturing process in order to optimize the settingtime of the hydraulically settable mixture.

J. Coatings

It is within the scope of the present invention to coat the extrudedhydraulically settable objects with sealing materials, paints, and otherprotective coatings. Appropriate coatings include calcium carbonate,melamine, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate,polyacrylate, hydroxypropylmethylcellulose, polyethylene glycol,acrylics, polyurethane, polyethylene, synthetic polymers, polylacticacid, Biopol® (a polyhydroxybutyrate-hydroxyvalerate copolymer), waxes(such as beeswax or petroleum based wax), elastomers, kaolin clay,polyacrylates, and synthetic polymers including biodegradable polymers.Biopol® is manufactured by ICI in the United Kingdom.

For example, a coating comprised of sodium silicate, which is acidresistant, is a particularly useful coating. Resistance to acidity isimportant, for example, where the extruded article is exposed tosubstances having a high acid content. Where it is desirable to protectthe extruded article from basic substances, the extruded objects can becoated with an appropriate polymer or wax, such as are used to coatpaper or paperboard products. If the extruded articles are intended tocome into contact with foodstuffs the coating material will preferablycomprise an FDA-approved coating.

The coatings may be applied to the extruded articles using any coatingmeans known in the art. Coatings may be applied by spraying the extrudedobject with any of the above-referenced coating materials, or it may beadvantageous to apply the coating by dipping the article into a vatcontaining an appropriate coating material. In the case where a coatingmaterial is sprayed onto the surface of a generally flat or regularlycurved object, the coating material may be spread or smoothed by meansof a straight or curved doctor blade which is held a particular distanceabove the object, or which rides directly on the surface. In addition,coatings may be coextruded along with the extruded object in order tointegrate the coating process with the extrusion process.

II. EXTRUDING HYDRAULICALLY SETTABLE MIXTURES

The basic structural component of the extruded articles of the presentinvention is the hydraulically settable matrix, which is formed from thereaction products of a hydraulically settable binder and water. Withinthe basic structural matrix are incorporated other components which addadditional characteristics and properties, such as fibers, aggregates,rheology-modifying agents, dispersants, and set accelerators. Using amicrostructural engineering and materials science approach makespossible the ability to include these various ingredients in a varietyof amounts and proportions in order to build into the mixture thedesired properties of form-stability and ultimate strength, toughness,and other performance criteria of the final hardened product.

The basic steps involved in the extrusion of hydraulically settablemixtures are as follows: (1) choosing the desired qualities andattributes of the article to be extruded from a hydraulically settablemixture, including size and strength properties; (2) selecting thedesired parameters of an appropriate extrusion process, including thetype of extruder, the die orifice shape, and the extrusion pressure,speed, and temperature; (3) determining the optimum composition andrheology, or range of rheologies, of an appropriate hydraulicallysettable mixture tailored to the desired qualities and attributes of thearticle and the desired parameters of the extrusion process; (4)preparing a suitable hydraulically settable mixture having theappropriate composition and rheology; (5) extruding the hydraulicallysettable mixture into the desired articles, or precursors to articlesthat can be further shaped into the desired articles; and (6) allowingthe extruded article, or later shaped article, to harden into the finalcured article. Optionally, the curing process may be accelerated by, forexample, autoclaving or by placing a partially hardened article into ahigh humidity environment.

A. Designing the Desired Qualities of the Article

Using the compositions and methods set forth herein, a wide variety ofarticles may be mass produced in high volume by extruding ahydraulically settable mixture into the desired shape of the article, orinto a precursor shape that may be further shaped into the desiredarticle. The articles formed by using the extrusion methods of thepresent invention are characterized as having high compressive, tensile,and flexural strength, as well as high particle packing density of thesolid aggregate and hydraulically settable binder particles. Thisresults in a more dense and less porous hydraulically settable materialthan has been heretofore possible. This results in an article having lowpenetrability and low diffusion of moisture. These characteristics arepossible using a microstructural engineering approach in order to designinto the material beforehand the desired properties and performancecriteria.

The high particle packing density of the extruded articles results from(1) the selection of aggregate particles having a predetermineddistribution of sizes and shapes in order to optimize the naturalparticle packing density, and (2) the extrusion of the hydraulicallysettable material under generally high pressures, which force theparticles into an even higher packing density than the natural packing,particularly where a there is an initial deficiency of water.

The high particle packing density and low water to hydraulicallysettable binder ratio that results from having an initial deficiency ofwater yield extruded articles having very low porosity and, hence, highstrength according to the Strength Equation. The use of dispersantsallows for the inclusion of even less water initially in order to createa more water deficient hydraulically settable mixture which will,nevertheless, be capable of being extruded under pressure.

The type of aggregate that will be used will depend largely on thedesired strength and density criteria of the final cured article, aswell as cost. Aggregates such as crushed sand, crushed granite, crushedbasalt, silica, gypsum, and clay are extremely inexpensive and cangreatly reduce the cost of manufacturing an extruded article therefrom.Such aggregates are also characterized as having high density and highcompressive strength.

The inclusion of a hydraulically settable binder such as portland greyor portland white cement will yield a final cured product that isgenerally waterproof and which will resist penetration by water andother liquids. Nevertheless, other hydraulically settable binders, suchas gypsum hemihydrate, are less water resistant and will yield a finalcured article having lower resistance to water. In the event that a morewater resistant article is desired, it may be advantageous to apply anappropriate coating onto the surface of the extruded article.

The inclusion of fibers and other high strength fillers can greatlyincrease the tensile and flexural strength of the final cured articles.The tensile strength may be stronger along one or more vectors or beevenly distributed depending on whether the fibers are aligned orrandomly dispersed throughout the hydraulically settable matrix. Theextrusion process itself will tend to orient the fibers in the directionof extrusion.

Different fibers have greatly varying degrees of tear and burststrength, flexibility, tensile strength, ability to elongate withoutbreaking, and stiffness. The type of fiber that will be incorporatedinto the hydraulically settable material will depend on the desiredproperties of the article. In order to obtain the advantageousproperties of different types of fibers it may be preferable in somecases to combine two or more different kinds of fibers within thehydraulically settable material.

In light of the foregoing, the cured extruded articles will preferablyhave a tensile strength greater than about 15 MPa. In many cases,depending on the mix design, water content, and extrusion pressure, itwill be possible to obtain extruded articles having tensile strengths ofabout 30 MPa or greater and, in some cases, of about 50 MPa or greater.Because of the ability to remove a large percentage of the interstitialvoids which are normally found within most cementitious products, thecured extruded hydraulically settable materials of the present inventionwill have a tensile strength to compressive strength ratio of about 1:7,which is higher than conventional concrete products, which typicallyhave a tensile strength to compressive strength ratio of only about1:10. Moreover, where high tensile strength fibers are employed insufficient quantities, it is possible, according to the presentinvention, to obtain cured hydraulically settable materials which have atensile strength to compressive strength ratio of about 1:3.

Because of the ability to extrude relatively thin-walled articles havingrelatively large internal cavities, it is possible for such extrudedarticles to have relatively low bulk densities. Extruded articles havinga multicellular structure will preferably have a bulk density less thanabout 1.5 g/cm³. Because of the ability to extrude multicellulararticles having wall thickness to cavity ratios that are far lower thanwhat is presently possible in the art, it is possible to extrudearticles having bulk densities of about 0.7 g/cm³ or lower and, in somecases, of about 0.3 g/cm³ or lower. Whether an extruded article willhave a lower, intermediate, or higher bulk density will generally dependon the desired performance criteria for a given usage, and will usuallydepend on the ratio of the volumes of the solid walls of the article andinternal cavities therein. The specific gravity of the solid walls ofthe articles will generally remain within the ranges stated herein.

In light of the foregoing, the extruded articles of the presentinvention will usually have significantly higher tensile strength tobulk density ratios compared to prior art cementitious articles. Theextruded articles will preferably have a tensile strength to bulkdensity ratio greater than about 5 MPa-cm³ /g, more preferably greaterthan about 15 MPa-cm³ /g, and most preferably greater than about 30MPa-cm³ /g.

B. Selecting the Extrusion Process

The type of extrusion process that will be employed will vary dependingon the nature of the hydraulically settable mixture being extruded, aswell as the desired properties of the extruded article. Although thehydraulically settable mix designs of the present invention havecarefully controlled rheology and plastic-like properties, which makethem suitable for other molding processes, the essential feature of theproducts of the present invention is that they can be continuouslyextruded into extruded articles that are form-stable immediately or veryshortly after the extrusion process. The continuous nature of extrusionprocess allows for the formation of a wide variety of articles in aneconomical and inexpensive fashion.

As stated above, a combination of particle packing density, waterdeficiency, and compression during the extrusion process creates ahydraulically settable mixture with a discontinuous rheology. Animportant criterion in the extrusion process is providing an extrudercapable of exerting the proper pressure or range of pressures for agiven mix design. Pressure within the proper range is necessary in orderto increase the particle packing density, and concomitantly decrease thevolume of interstitial space, which decreases the effective waterdeficiency of the mixture. This allows for better lubrication of theparticles and increased workability and flow properties.

The best properties are generally obtained by exerting a pressure whichis commensurate with the levels of particle packing, water deficiency,and aggregate strength within the mixture. Too little pressure might beinadequate to impart adequate flow properties to the hydraulicallysettable mixture. Conversely, too much pressure may pulverize certainaggregates within the hydraulically settable mixture, while compressingthe mixture to the point of having excess water. Excess water may, insome cases, reduce the viscosity and/or yield stress of thehydraulically settable mixture to the point that it will lack sufficientform-stability.

Depending on the amount of pressure that is desired and the amount oftype of shear to be exerted onto the hydraulically settable mixture,either a piston-type or auger-type extruder can be used. The advantageof the piston-type extruder as shown in FIG. 1 is the greater amount ofpressure which can be applied. In order to apply very high pressures,including those of up to 100,000 psi, the only current possibility is touse a piston extruder.

Auger-type extruders, as shown in FIG. 2, typically do not exert as muchpressure as a piston extruder, and are preferred where extremely highpressures are unnecessary. Auger-type extruders have the advantage ofimparting internal shear by the turning of the auger screw and theability to apply a vacuum or negative pressure to the hydraulicallysettable mixture within the auger extruder to remove unwanted air withinthe mixture on a more continuous basis. The double auger extruder hasbeen used mainly on an experimental basis and includes two parallelauger screws, which allow for a wider extruder die and greater extrusionpressures. In most other respects, the twin auger extruder is similar tothe single auger extruder.

However, where hydraulically settable mixtures that are very deficientin water are used, it will often be necessary to use a piston extruderin order to exert higher pressures on the mixtures and cause them toflow. In such cases, the hydraulically settable mixture might appear asa dry-looking, granulate material prepared by mixing the componentswithin a drum. The granulates are placed into a piston extruder chamber,put under a vacuum, and then compacted under high pressure by the pistonin order to extruded the material. The use of a duel-batch pistonextruder allows for a semi-continuous extrusion process.

A currently preferred system for large scale mixing and extrusion in anindustrial setting involves equipment in which the materialsincorporated into the hydraulically settable mixture are automaticallyand continuously metered, mixed, de-aired, and extruded by either asingle or twin auger extruder apparatus. Either a single or twin augerextruder apparatus has sections with specific purposes, such as lowshear mixing, high shear mixing, vacuuming, and pumping. A single ortwin auger extruder apparatus has different flight pitches andorientations which permit the sections to accomplish their specificpurposes.

The main types of extruders include either the clay or the plastic orfood extruder. A clay extruder usually has an extruder having a veryhigh pitch and flight height, the pitch often being 90° from theextruder die. The high pitch increases the amount of surface area of theinterface between the auger blades and the material to be extruded, andincreasing the pitch and resulting surface area increases the pressureand shear rate of the extruder.

On the other hand, a plastic or food extruder has a much lower flightheight and pitch compared to the clay extruder. In this case, thepressure and shear rate are controlled by increasing or decreasing theRPM of the auger screw. Of course, increasing the RPM of the auger screwof a clay extruder will also increase the pressure and shear rate.

C. Designing The Hydraulically Settable Mixture

The two main criteria used to design an appropriate hydraulicallysettable mixture are the desired rheology of the mixture before, during,and after the extrusion process and the desired properties of the finalhardened extruded article. As set forth above, the rheology of thehydraulically settable mixture is preferably designed so that themixture will be able to flow and be extruded when subjected to theparameters of the given extrusion process, and thereafter be form-stableimmediately or shortly after being extruded.

As previously discussed, the rheology of the hydraulically settablemixture may be determined initially by controlling (1) the particlepacking density of the aggregate and hydraulically settable binderparticles, (2) the amount of added water, including the level of waterdeficiency, and (3) the identity and amount of any organic polymerrheology-modifying agents, plasticizers, or dispersants. How thesematerials and conditions are interrelated has been discussed in detail.

In addition, the rheology of the hydraulically settable mixture may bealtered by the addition of shear forces to effect shear thinning orpseudo-plastic behavior of the water deficient mixture, as well as bycompressive forces which reduce the level of water deficiency by forcingthe aggregate and hydraulically settable binder particles into closerproximity. In light of this, the level of water deficiency shouldcorrelate to the amount of compression and shear force that will beexerted on the hydraulically settable mixture. That is, less water may,as a general matter, be added initially as the amount of compressive andshear forces associated with the extrusion process are increased.

The release of the compressive and shear forces upon extruding thehydraulically settable mixture into the desired article results in aform-stable article held together by internal cohesion of the capillarywater or meniscuses. However, these internal forces are dependent uponthe amount of water within the capillaries of the material within theextruded article. If the amount of water is too low, there will beinsufficient capillary forces to maintain adequate cohesion. Conversely,if the amount of water is too high, the material will have inadequateyield stress to remain form-stable. The amount of water that remainswill be a function of the amount of water added initially, as well asthe level of compression during the extrusion process.

Upon hydrating, the extruded hydraulically settable material willdevelop its final strength properties. The compressive strength of thematerial may be determined by the Strength Equation, and is mainly afunction of the porosity of the final hardened material. This is alsotrue for the tensile and flexural strengths of the hardened material toa certain extent. Porosity can be reduced by increasing the initialparticle packing density and by decreasing the amount of water that isadded initially (or increasing the water deficiency). The level ofcompressive strength that is desired will depend on the particularperformance criteria of the desired article.

In addition, the compressive strength can be increased by using strongeraggregates. Conversely, lighter weight aggregates can be employed when aless strong, but lighter weight article is desired. The tensile andflexural strengths may be altered by adding varying amounts of fiber.Shorter, stronger fibers, such as ceramic fibers, will generally yield arelatively stiff final hardened article with high tensile and flexuralstrength. Other fibers, such as cellulosic fibers, have lower tensilestrength but are less expensive and more flexible and may be adequatewhere properties of flexibility and toughness are more important.

1. Optimizing the Particle Packing Density

Achieving an optimized particle packing arrangement within the solidmaterials of the hydraulically settable mixture is desirable in order toobtain a hydraulically settable mixture having the desired rheologicaland final strength properties. Once the particle packing density of adry mixture is determined, it is then possible to calculate how muchwater should be added to the mixture in order to achieve the desiredlevel of water deficiency. A detailed description of the theory, models,and steps necessary to accurately and reproducibly optimize theparticle-packing density of the solid particles with a hydraulicallysettable mixture is set forth in copending U.S. application Ser. No.08/109,100, entitled: "Design Optimized Compositions and Processes forMicrostructurally Engineering Cementitious Mixtures," and filed Aug. 18,1993, in the name of Per Just Andersen, Ph.D. and Simon K. Hodson. Forpurposes of disclosure, this application is incorporated herein byspecific reference. In addition, mathematical and graphic models used todetermine and quantify the particle-packing density of a mixture is setforth in V. Johansen and P. J. Andersen, "Particle Packing and ConcreteProperties" at 118-22, Materials Science of Concrete II (The AmericanCeramic Society, Inc., 1991). For purposes of disclosure, this articleis incorporated herein by specific reference.

In order to achieve a desired packing density of the various particleswithin the hydraulically settable mixture, including the hydraulicallysettable binder particles and the aggregates, the particles will have atleast two size ranges. In order to increase the particle-packing densityto higher theoretical limits, it may be preferable in some cases to havethree or more different size ranges of particles. For purposes ofparticle packing, mixtures that contain two different size ranges ofparticles are referred to as "two-component systems", those that havethree different particle size ranges are referred to as "three-componentsystems", and so on. For simplicity, the two different components of atwo-component system may be referred to as the fine and coarsecomponents, while in the three-component system they may be referred asthe fine, medium, and coarse components.

In order to obtain an optimized level of particle packing, it ispreferable for the average particle size within one size range to be atleast seven and one-half times the particle size of the next smallestparticle range, more preferably at least about ten times, and mostpreferably at least about twelve and one-half times. (In many cases theratio may be greater.) For example, in a two-component system, it willbe preferable for the average particle size of the coarse component tobe at least about seven and one-half times the average particle size ofthe fine component. Likewise, in a three-component system, it will bepreferable for the average particle size of the coarse component to beat least seven and one-half times the average particle size of themedium component, which will likewise preferably be at least seven andone-half times the size of the fine component. Nevertheless, as moredifferently sized particles are added, the ratio between the particlesize magnitudes need not always be this great.

In a three-component system, it will be preferable for the fineaggregate particles to have diameters within a range from about 0.01microns to about 2 microns, with a medium aggregate particle to havediameters in a range from about 1 to about 20 microns, and for thecoarse aggregates to have a diameter within a range from about 100microns to about 2 mm. In a two component system, any two of theseranges may be preferable. Larger and smaller diameter particles may beused, as well as particles within different ranges, depending on thenumber of different particle types.

The term "type" as used in the specification and appended claims withregard to aggregate, hydraulically settable binder, and other solidparticles is intended to include both the kind of material used and theranges of the particle sizes. For example, although coarse aggregatesusually have particle diameters in a range from about 100 microns toabout 2 mm, one type of coarse aggregate may have a particle size rangefrom about 200 to about 500 microns while a second type may have aparticle size range from about 700 microns to about 1.2 mm. As statedherein, optimal particle packing of a mixture can be obtained byselectively combining different types of aggregates. Each type ofaggregate has a defined average particle size; studies have found,however, that particle gap grading leads to good packing but lowworkability compared to continuous gradation.

In general, a two-component (or binary) packing system will seldom havean overall packing density higher than about 80%, while the upper limitfor a three-component (or ternary) system is about 90%. To obtain higherparticle packing it will be necessary in most cases to add four or morecomponents, although having broader and more optimized particle sizesamong two- or three-component systems can yield higher overall particlepacking than 80% and 90%, respectively.

The hydraulically settable binder used in the present invention isusually a hydraulic cement, gypsum, or calcium oxide and may, in somecases, comprise fly ash or silica fume. Hydraulic cement ischaracterized by the hydration products that form upon reaction withwater. Hydraulic cements generally have particle sizes ranging from 0.1μm to 100 μm. Portland cement, Type 1 has an average particle size in arange from about 10 to about 25 microns.

The types of aggregates and hydraulically settable binders used in thepresent invention are further defined by the average diameter size (d')and the natural packing density (φ) of the types of particles. Thesevalues are experimentally determined and are necessary for calculatingthe packing density of the resulting hydraulically settable mixture.

The natural packing density of each type of material is determined byfilling the material into a cylinder having a diameter of at least 10times the largest particle diameter of the material. The cylinder isthen tapped against a hard surface until the material is fullycompacted. By reading the height of compacted material in the cylinderand the weight of material, the packing density is calculated accordingto the formula: ##EQU1## Where, W_(M) =weight of the material,

SG_(M) =specific gravity of the material, and

V_(M) =volume of the material.

Of course, two or more types of hydraulically settable binder may alsobe added to a mixture. The particle size of the hydraulically settablebinder is usually so small, however, that the combination of differenttypes of hydraulically settable binders generally does not significantlyaffect the packing density of the mixture. Nevertheless, in somesituations the combination of different types of hydraulically settablebinders may be relevant. In these situations, the types of hydraulicallysettable binder can be represented as a pseudo-particle in the samemanner as for fine and coarse aggregate.

The above described process teaches a method for determining the packingdensity for all possible combinations of a given feed stock. With regardto the rheological effect, increasing the particle packing densityallows for the inclusion of less water while maintaining the same levelsof workability and plastic-like behavior of the mixture. In addition toimproving the rheological properties of the mixture while in the greenstate, maximizing particle packing density also increases the strengthof the final cured product by reducing the amount of interstitial spacefilled either by air, water, or a combination of both (according to theStrength Equation).

Nevertheless, it should be understood that "optimizing" the particlepacking system will not necessarily be achieved by simply maximizing theparticle packing density. As a general rule, maximization of particlepacking density tends to increase the desired properties which areachieved through particle packing. However, restraints such as costand/or availability of particular aggregates might warrant a lowerparticle packing density while still obtaining a mixture with adequaterheological properties for a particular purpose.

Although it has been recognized that increasing the particle packingdensity aids in controlling the rheological properties of ahydraulically settable mixtture, the maximum packing density in theprior art has been about 65%. In contrast, through the particle packingtechniques described above, it is possible to obtain natural particlepacking densities greater than 65%, and even as high as 99%.

In general, the particle packing density will preferably be within arange from about 0.65 to about 0.99, more preferably between about 0.70and about 0.95, and most preferably between about 0.75 and about 0.90(The added cost of achieving 99% particle packing efficiency is oftenprohibitive. Therefore, most preferred packing densities are somewhatless).

FIG. 1 illustrates the concept of particle packing by showing across-section of particles which have been efficiently packed together(particle packing density of 0.70). From FIG. 1, it can be seen that thespaces between the larger aggregate particles that would normally beoccupied by air are instead occupied by smaller aggregates. Moreover,the space between the larger and smaller particles which would normallybe occupied by air are in turn occupied by yet smaller sized aggregateparticles. In this way, the volume of interstitial air between theparticles is greatly reduced, while the particle packing density isgreatly increased.

FIG. 2 graphically illustrates and quantifies the actual packing densityby showing how in a typical packing system (particle packing density of0.70) the overall volume of the mixture is distributed between solidparticles (70%) and interstitial space (30%). It is this interstitialspace into which water is added in order to lubricate the individualparticles so that the hydraulically settable mixture will have adequateworkability and flow properties, particularly when the packing densityis temporarily increased by extruding the mixture under increasedpressure.

C. Water Deficiency

As stated above, the amount of water which will be added to any givenhydraulically settable mixture should be carefully measured in order toobtain the desired properties of workability and rheology. It will beunderstood, however, that the amount of water to be added to any givenmixture will often have less to do with the volume, or even the mass, ofthe dry hydraulically settable mixture but directly corresponds to thepacking density, more particularly the amount of interstitial voidswithin the mixture.

To better illustrate this point, reference is made to FIGS. 3A and 3B,which show two different particle packing systems having the sameoverall volume and which are both 0% deficient in water. That is, justenough water has been added to completely fill the interstices betweenthe particles. Both of these mixtures will have similar rheologies eventhough they have quite varying amounts of water. As shown graphically inFIGS. 3A and 3B, the mixture having a packing density of 65% (FIG. 3A)has seven times the interstitial water of the mixture having 95% packingdensity (FIG. 3B). (Of course, it would also be predicted that themixture with the higher packing density will have greater strength whencured, according to the Strength Equation.)

FIG. 4 shows an optimized particle packing system in which there is a50% deficiency of water, that is, only half of the interstitial spacehas been filled with water (50% of the space, or 15% of the overallmixure by volume). As a matter of comparison, two hydraulically settablemixtures which have the same overall volume and the same volume of addedwater will have differing levels of water deficiency whenever theirparticle packing density differs. The lower the packing density thegreater the water deficiency since there is more interstitial space tobe filled.

FIG. 5 shows both pictorially and graphically how the application ofpressure to a hydraulically settable mixture, such as by an extruder,causes the particles of the mixture to become more compacted, therebyincreasing their packing density. Because the particles and water areessentially incompressible, the amount of interstitial voids greatlydecreases, while the amount of water available to lubricate theparticles apparently increases. Although air is extremely compressibleand would not significantly impede the compaction process describedabove, it is advantageous to remove the air by means of a vacuum inorder to prevent re-expansion of the air upon release of the compressiveforce.

Knowing just how much water should be added to any given hydraulicallysettable mixture must be carefully calculated prior to actually addingthe water and also verified once the water is added. As stated above,the hydraulically settable binder does not necessarily react with all ofthe theoretical stoichiometric water necessary to hydrate the binder.Instead, some of this water actually fills the interstitial space, atleast temporarily until it reacts with the hydraulically settable binderover time.

Of course, it should be understood that the level of water deficiency isnot the only determinant of the rheology of the hydraulically settablemixture. Other additives, such as dispersants and rheology-modifyingagents, greatly affect the viscosity, workability, and other rheologicalproperties of the mixture. One skilled in the art will be able to adjustthe level of water deficiency based on the amount of dispersant and/orrheology-modifying agent that has been added to the mixture to obtain ahydraulically settable mixture having the desired properties.

D. Preparing The Hydraulically Settable Mixture

As set forth above, any mixing means that is appropriate for aparticular manufacturing process will work well to achieve good particlepacking, although it is believed that the best particle packing densityis achieved by mixing together the aggregates and the hydraulicallysettable binder particles before any water has been added. Once thedesired amount of water is ready to be added, any appropriate mixingprocess may be used. A high shear mixer, such as those described morefully hereinafter, may be used to create a very homogeneous mixture. Akneader-mixer, such as a clay kneader, is often preferable where lowershear is desired. Finally, the materials may be mixed together andextruded using either a single or twin auger extruder. High frequencyvibration may be used in conjunction with any mixing process to aid inthe mixing of the components.

The currently preferred embodiment for preparing an appropriate moldablemixture in an industrial setting includes equipment in which thematerials incorporated into the moldable mixture are automatically andcontinuously metered, mixed (or kneaded), de-aired, and extruded by anauger extruder apparatus. It is also possible to premix some of thecomponents in a vessel, as needed, and pump the premixed components intoa kneading mixing apparatus.

A double shaft sigma blade kneading mixer with an auger for extrusion isthe preferred type of mixer. The mixer may be adjusted to have differentRPMs and, therefore, different shear for different components.Typically, the moldable mixtures will be mixed for a maximum of about 60minutes, and thereafter emptied from the mixer by extrusion.

In certain circumstances it may be desirable to mix some of thecomponents together in a high shear mixture in order to form a more welldispersed, homogeneous mixture. For example, certain fibers may requiresuch mixing in order to fully disagglomerate or break apart from eachother. High shear mixing results in a more uniformly blended mixture,which improves the consistency of the unhardened moldable mixture aswell as increasing the strength of the final hardened sheet. This isbecause high shear mixing more uniformly disperses the fiber, aggregateparticles, and binder throughout the mixture, thereby creating a morehomogeneous structural matrix within the hardened sheets.

High shear mixers useful in creating the more homogeneous mixtures asdescribed herein are disclosed and claimed in U.S. Pat. No. 4,225,247entitled "Mixing and Agitating Device"; U.S. Pat. No. 4,552,463 entitled"Method and Apparatus for Producing a Colloidal Mixture"; U.S. Pat. No.4,889,428 entitled "Rotary Mill"; U.S. Pat. No. 4,944,595 entitled"Apparatus for Producing Cement Building Materials"; and U.S. Pat. No.5,061,319 entitled "Process for Producing Cement Building Material". Forpurposes of disclosure, the foregoing patents are incorporated herein byspecific reference. High shear mixers within the scope of these patentsare available from E. Khashoggi Industries of Santa Barbara, Calif., theAssignee of the present invention.

Different mixers are capable of imparting differing shear to themoldable mixer. For example, a kneader imparts higher shear compared toa normal cement mixer, but is low compared to an Eirich Intensive Mixeror a twin auger food extruder.

It should be understood, however, that high shear, high speed mixing isgenerally efficacious only where the mixture has relatively lowviscosity. In those cases where it is desirable to obtain a morecohesive, plastic-like mixture, it may be desirable to blend some of theingredients, including water, in the high shear mixer and thereafterincrease the concentration of solids, such as fibers or aggregates,using a lower shear kneading mixer.

In many cases the order of mixing will impart different properties tothe hydraulically settable mixture. In a currently preferred embodimentin which both a dispersant and a rheology-modifying agent are used, itwill be preferable to first mix the hydraulically settable binder andwater together using a high shear mixer. The dispersant is preferablyadded after significant wetting of the hydraulically settable binderparticles has occurred. After the dispersant has been substantiallyadsorbed by the hydraulically settable binder particles, therheology-modifying agent is added to the mixture.

E. Extruding Articles From The Hydraulically Settable Mixture

Once the moldable mixture has been properly blended, it is thentransported to the extruder. Although the hydraulically settable mixdesigns of the present invention have o carefully controlled rheologyand plastic-like properties which make them suitable for other moldingprocesses, the essential feature of the products of the presentinvention is that they can be continuously extruded. It is thiscontinuous extrusion process which allows the formation of a widevariety of objects and shapes in an economical and inexpensive fashion.

As stated above, a combination of particle packing density, waterdeficiency, and compression during the extrusion process creates ahydraulically settable mixture with discontinuous rheologicalproperties. Hence, an important criterion in any extrusion process ischoosing an extruder which is capable of exerting a carefullypredetermined pressure for any given mix design. This is because thecompressive forces of the extruder are responsible for temporarilyincreasing the particle packing density, which decreases the volume ofinterstitial space and decreases the effective water deficiency of themixture. This immediately translates into better lubricated particlesand increased workability and flow properties.

However, the best properties are generally obtained by exerting apressure which is commensurate with the levels of particle packing,water deficiency and aggregate strength within the mixture. Adding toolittle pressure would prevent the ability to impart adequate flowproperties to the hydraulically settable mixture. Conversely, adding toomuch pressure might also cause a number of problems, including thepulverization of certain aggregates within the hydraulically settablemixture, a tendency of the extruded material to burst out of theextruder die rather than continuously flowing out, or non-uniformity offlow through the die.

Depending on the amount of pressure that is desired and the amount oftype of shear to be exerted onto the hydraulically settable mixture,either a piston-type or auger-type extruder can be used. An auger-typeextruder (FIG. 6) has certain advantages even though it cannot be usedto extrude at the same high pressures as a piston extruder. Theseadvantages include continuous internal shear which is applied by theturning auger screw, as well as greater ease in continuously applying avacuum or negative pressure to the hydraulically settable mixture withinthe auger extruder to remove any unwanted air within the mixture. Insome cases, an apparatus capable of both mixing and extruding themoldable mixture may be used in order to streamline the operation andminimize the coordination of the various o components within the system.The advantage of the piston-type extruder as shown in FIG. 7 is thegreater amount of pressure which can be applied. In order to apply veryhigh pressures, even up to 100,000 psi, the only currently known to usepossibility is a piston extruder.

Reference is now made to FIG. 6, which is a closeup view of an augerextruder 20, which includes a feeder 22 that feeds the moldable mixtureinto a first interior chamber 24 within the extruder 20. Within thefirst interior chamber 24 is a first auger screw 26 which exerts forwardpressure on and advances the moldable mixture through the first interiorchamber 24 toward an evacuation chamber 28. Typically, a negativepressure or vacuum will be applied to the evacuation chamber 28 in orderto remove unwanted air voids within the moldable mixture.

Thereafter, the moldable mixture will be fed into a second interiorchamber 30. A second auger screw 32 will advance the mixture toward adie head 34 having a transverse slit 36 with a die width 38 and a diethickness 39. The cross-sectional shape of the die slit 36 is configuredto create a sheet of a desired width and thickness that will generallycorrespond to the die width 38 and die thickness 39.

Alternatively, as seen in FIG. 7, the extruder may comprise a pistonextruder 20' instead of an auger extruder 20. A piston extruder utilizesa piston 22' instead of an auger screw 22 in order to exert forwardpressure on and advance the moldable mixture through the interiorchamber 24'. An advantage of using a piston extruder is the ability toexert much greater pressures upon the moldable mixture. Nevertheless,due to the highly plastic-like nature of mixtures typically employed inthe present invention, it is not generally necessary, or evenadvantageous, to exert pressures greater than those achieved using anauger extruder.

A currently preferred system for large scale mixing and extrusion in anindustrial setting involves equipment in which the materialsincorporated into the hydraulically settable mixture are automaticallyand continuously metered, mixed, de-aired, and extruded by a twin augerextruder apparatus. A twin auger extruder apparatus has sections withspecific purposes, such as low shear mixing, high shear mixing,vacuuming, and pumping. A twin auger extruder apparatus has differentflight pitches and orientations which permits the sections to accomplishtheir specific purposes.

It is also possible to premix some of the components in a vessel, asneeded, and pump the premixed components into the twin auger extruderapparatus. The preferable twin auger extruder apparatus utilizes uniformrotational augers wherein the augers rotate in the same direction.Counter-rotational twin auger extruders, wherein the augers rotate inthe opposite directions, accomplish the same purposes. A pug mill mayalso be utilized for the same purposes. Equipment meeting thesespecifications are available from Buhler-Miag, Inc., located inMinneapolis, Minn.

The amount of pressure that is applied in order to extrude the moldablemixture will generally depend on the pressure needed to force themixture through the die head, as well as the desired rate of extrusion.The rate of extrusion should be carefully controlled in somecircumstances in order for the rate of formation of the extruded articleto correspond to the rate of subsequent processing steps, such ascutting and/or reformation of the extruded article. An important factorwhich will affect the optimum speed or rate of extrusion is the finalthickness of the extruded article. A thicker article contains morematerial and will require a higher rate of extrusion to provide thenecessary material. Conversely, a thinner article contains less materialand will require a lower rate of extrusion in order to provide thenecessary material.

The ability of the moldable mixture to be extruded through a die head,as well as the rate at which it is extruded, is generally a function ofthe rheology of the mixture, as well as the operating parameters andproperties of the machinery. Factors such as the amount of water,hydraulically settable binder, rheology-modifying agent, dispersant, theparticle packing density, or the level of water absorption or reactionby the mixture components all affect the rheological properties of themixture.

As set forth above, adequate pressure is necessary in order totemporarily increase the workability of the moldable mixture in the casewhere the mixture has a deficiency of water and has a degree of particlepacking optimization. In a mixture that is water deficient, the spaces(or interstices) between the particles contain insufficient water tolubricate the particles in order to create adequate workability underordinary conditions. However, as the mixture is compressed within theextruder, the compressive forces drive the particles together, therebyreducing the interstitial space between the particles and increasing theapparent amount of water that is available to lubricate the particles.In this way, workability is increased until the mixture has beenextruded through the die head, at which point the reduced pressurecauses the mixture to exhibit an almost immediate increase in stiffnessand green strength, which is generally desirable.

In light of each of the factors listed above, the amount of pressurewhich will be applied by the extruder in order to extrude the moldablemixture will preferably be in a range from about 10 bars to about 7000bars, more preferably in a range from about 20 bars to about 3000 bars,and most preferably in a range from about 50 bars to about 200 bars.

It will be understood that the extrusion of the moldable mixture throughthe die head will tend to unidirectionally orient the individual fiberswithin the moldable mixture along the "Y" axis, or in the lengthwisedirection of the extruded article.

As set forth above, it may also be desirable to co-extrude thehydraulically settable mixture with other materials in order to obtain,e.g., a laminate structure or an extruded product with other materialsimpregnated within the hydraulically settable matrix. Things which maybe co-extruded with the extrudable hydraulically settable mixtures ofthe present invention include another hydraulically settable mixture(often having different or complementary properties), a fibrous mat,continuous fibers, coating materials, polymers, clays, graphite (formaking a pencil), continuous fibers, or strips, wires, or sheets ofalmost any other material (such as metal). It has been found that byjoining together, for example, a hydraulically settable sheet and afibrous mat by co-extrusion that the final product exhibits synergisticresults of strength, toughness, and other performance criteria.

F. Accelerated Drying

Although the hydraulically settable materials of the present inventionare capable of quickly gaining high green strength, it may yet bedesirable to accelerate further the hardening or stiffening of theextruded materials. This can be accomplished by applying heat to furtherremove some of the water within the hydraulically settable mixture,particularly from the surface where the greatest amount of greenstrength is often desired. Heating is especially desirable where thereis an excess of water within the mixture in order to increase theviscosity and yield stress of the extruded article and impart thedesired rapid form-stability.

Because of the nature of extrusion, it will usually not be advantageousto overheat the extruder die above a certain temperature in order toremove water during the extrusion process. Overheating the die mightcause the extruded mixture to expand or form pockets of high pressuresteam that can cause the hydraulically settable mixture to "explode" outof the extruder die. (Nevertheless, some degree of heating may bedesirable in order to reduce the friction between the extruded materialand the extruder die by forming a steam barrier.) By careful control ofthe rheology of the hydraulically settable mixture and appropriateheating of the extruder die, it is generally possible to obtain extrudedarticles having strength to allow it to be handled immediately afterextrusion.

G. Accelerated Curing

In those cases in which the extruded hydraulically settable mixture isso water deficient that there is insufficient water to adequatelyhydrate the cement or other hydraulically settable binder, it might beadvantageous to expose the extruded object to water or air having highhumidity. The hygroscopic nature of typical binders, particularlyhydraulic cement, allows the binder to literally absorb the necessarywater of hydration from the air. Although this would occur naturally inany event (at least in the case of hydraulic cement), exposing the verywater deficient extruded object to air having high humidity greatlyincreases this water absorption process and the rate of hydration of thebinder particles. In particular, autoclaving may be used in order togreatly increase the strength of the final cured article.

III. EXAMPLES OF THE PREFERRED EMBODIMENTS

To date, numerous tests have been performed comparing the rheologicaland extrusion properties of various hydraulically settable mixtures ofvarying composition. Below are specific examples of compositions whichhave been extruded according to the present invention. In addition, anumber of hypothetical, or "prophetic", examples have been includedbased on actual mix designs that have been extruded or which would beexpected, based on experience, to posses the properties describedhereinafter. The actual examples are written in the past tense while thehypothetical examples are written in the present tense in order todistinguish between the two.

In general, the examples are directed to hydraulically settable mixtureswhich employ varying levels of water deficiency and particle packingefficiency, along with varying amounts of, for example, hydraulicallysettable binder, aggregates, fibers, rheology-modifying agents, andother admixtures in order to obtain mixtures having varying flowproperties when extruded under pressure, and varying degrees ofform-stability once the article has been extruded and the pressurereleased.

EXAMPLES 1-9

Hydraulically settable mixtures having 4 kg of portland cement Type 1, 6kg fine silica sand, 50 g Tylose® FL 15002, and varying amounts of waterwere prepared and then extruded through a die using a piston extruder.The fine silica sand had a natural packing density of about 0.55 and aparticle size in the range from about 30-50 microns. When mixed withportland cement Type 1, which has an average particle size in a rangefrom about 10-25 microns, the resulting dry mixture had a particlepacking density of about 0.65, which represents only a moderate increaseover the natural packing density of each. The natural packed volume ofthe cement and sand was 5.504 liter, with a porosity of 1.924 liter.

The amount of water in the mixtures was varied as follows in order todetermine the extrudability of the mixture at varying levels of waterdeficiency:

    ______________________________________                                        Example Water     % Deficient Extrusion Pressure                              ______________________________________                                        1       3.0 kg    (55.9%)      15 psi                                         2       2.5 kg    (29.9%)      15 psi                                         3       1.924 kg  0%           45 psi                                         4       1.905 kg  1.0%         100 psi                                        5       1.65 kg   14.2%        300 psi                                        6       1.443 kg  25.0%        820 psi                                        7       0.962 kg  50.0%       1639 psi                                        8       0.60 kg   68.8%       2131 psi                                        9       0.40 kg   79.2%       3278 psi                                        ______________________________________                                    

In Examples 1 and 2, the numbers in parentheses under the heading "%Deficient" indicates that an excess of water was used. That is, morewater than the volume of interstitial space (or porosity, which was1.924 liter) was added. As a result, these mixtures were characterizedas "very fluid" and could not be extruded with sufficientform-stabilitty so that the extruded objects would maintain their shapewithout external support. Similarly, although Examples 3 and 4 were lessfluid and were characterized as "very soft" they could not be extrudedinto form-stable objects that would completely maintain their shapewithout external support. However, as the amount of water was furtherdecreased, thereby increasing the water deficiency, the form-stabilityof the extruded material increased to the point where an extruded objectwould maintain its shape without external support.

The mixture of Example 5 was characterized as "soft" but could beextruded at relatively low pressure into an object having goodform-stability. The mixtures in Examples 6-9 could be extruded byincreasing the extrusion pressure as the amount of water was decreased,with increasing form-stability being observed as the amount of waterdecreased. As the water deficiency and extrusion was increased, thelevel of compaction of the mixture also increased, which resulted ingreater packing of the particles together and higher density of theextruded material. After each of the mixtures was allowed to harden, thehardened material for each example had the following tensile strengths,respectively, expressed in MPa: 2.4, 3.1, 5.2, 15.2, 28.2, 30.3, 32.2,35.0, and 38.0.

The mixtures of Examples 5-9 were successfully extruded into honeycomb(i.e., multicellular) structures, bars, and window frames. The mixturesof Examples 6-9 were also extruded into pipes of varying wall thickness.The pipe extruded from the mixture of Example 7 had a wall thicknessthat was 25% of the pipe cavity; the pipe extruded from the mixture ofExample 8 had a wall thickness that was 15% of the pipe cavity; and thepipe extruded from the mixture of Example 9 had a wall thickness thatwas 10% of the pipe cavity.

EXAMPLE 10-13

To the mixtures of Examples 5-9 are added the following amounts offiber, expressed as a percentage by volume of the total solids contentof the hydraulically settable mixture:

    ______________________________________                                               Example                                                                              Fiber                                                           ______________________________________                                               10     1%                                                                     11     2%                                                                     12     3%                                                                     13     4%                                                              ______________________________________                                    

The type of fiber that will be added depends on the properties andperformance criteria of the extruded article. In general, however,increasing the tensile strength of the fiber will increase the tensilestrength of the extruded article. Nevertheless, other factors such asaspect ratio, length, and reactivity with the hydraulically settablebinder will affect the level of anchoring or pull-out of the fiberswithin the hydraulically settable matrix when subjected to stresses andstrains. As the amount of fiber is increased, the tensile strength andductility of the hardened extruded article also increase.

EXAMPLE 14

The procedures of Examples 1-9 were repeated except that the amount ofTylose® FL 15002 within the hydraulically settable mixture was increasedto 100 g prior to extrusion. The increased amount of Tylose® aided theextrusion process by increasing the lubrication between the particlesthemselves and between the particles and the extruder walls and diehead.In addition, the increased Tylose® increased the form-stability of theextruded articles somewhat, although not two-fold.

EXAMPLE 15

The procedures of Examples 1-9 were repeated except that 160 g ofsulfonated naphthalene-formaldehyde condensate was added to the mixtureas a dispersant. First the hydraulic cement, water, dispersant and atleast part of the aggregate were mixed together using a high shear mixerfor about 10 minutes. Afterward, the Tylose® FL 15,002 and the remainingaggregate, if any, were mixed into the mixture using a low shear mixer.The dispersant allowed for the obtaining of a more fluid mixture whilemaintaining the same level of water.

The resulting hydraulically settable mixtures have lower viscosity,which made them more easily extruded using lower pressures, compared tothe mixtures of Examples 1-9. However, the extruded articles weregenerally less form stable than their counterparts obtained in Examples1-9. Nevertheless, significantly less water was required to obtain amixture having the same level of extrudability and form stability in thepresent example compared to in Examples 1-9. This yielded final curedarticles having higher strength due to the reduced amount of waterwithin the hydraulically settable mixtures, according to the StrengthEquation.

EXAMPLE 16

The procedures of Examples 1-9 and 15 were repeated, except that 0.8 kgof silica fume was also added to each of the mixtures. Because of thehigh specific surface area of silica fume, the mixtures which includedsilica fume had better dispersion, particularly where a dispersant wasadded to the mixture.

While the addition of silica fume would be expected to result in amixture requiring more water to obtain the same level of workability, itturns out that the extremely small particle size of the silica fumerelative to the other particles within the hydraulically settablemixtures greatly increased their particle packing densities.Consequently, the mixtures had significantly lower porosities, whichdecreased the amount of water needed to lubricate the particles. As aresult, the extrudability of the mixtures containing silica fume wassimilar to those which did not include silica fume. However, the silicafume increased the yield stress and cohesive nature of the mixtures,which increased the form stability of the extruded articles madetherefrom.

In the following examples, the particle sizes of the silica sandaggregate were increased in order to increase the packing density of theresulting mixture. The increased particle packing densities that werethus obtained resulted in extruded articles of higher strength. Thisgoes against the conventional wisdom, which teaches the use of thefinest particle size available in order to increase the density, andhence the strength, the final hardened article. In contrast, byprogressively increasing the size of the silica sand particles, whichincreased the ratio of the size of the aggregate particle to the cementparticles to within the preferred and more preferred ranges, the densityof the mixture actually increased.

EXAMPLES 17-36

The same amounts and types of hydraulically settable binder andaggregate were used according to Examples 1-9, except that the amount ofadded water was varied in much smaller gradations as follows:

    ______________________________________                                        Example       Water   % Deficient                                             ______________________________________                                        17            3.0 kg  (55.73%)                                                18            2.8 kg  (45.35%)                                                19            2.6 kg  (34.97%)                                                20            2.4 kg  (24.59%)                                                21            2.2 kg  (14.20%)                                                22            2.0 kg  (3.82%)                                                 23            1.8 kg  6.46%                                                   24            1.6 kg  16.94%                                                  25            1.4 kg  27.32%                                                  26            1.2 kg  37.71%                                                  27            1.0 kg  48.09%                                                  28            0.9 kg  53.23%                                                  29            0.8 kg  58.47%                                                  30            0.7 kg  63.66%                                                  31            0.6 kg  68.85%                                                  32            0.5 kg  74.04%                                                  33            0.4 kg  79.24%                                                  34            0.3 kg  84.43%                                                  35            0.2 kg  89.62%                                                  36            0.1 kg  94.81%                                                  ______________________________________                                    

The extrusion pressure needed to extrude the mixtures of these exampleswere similar to those needed to extrude the mixtures of Examples 1-9. Asabove, the mixtures in Examples 17-22 were too fluid to have adequateform-stability after being extruded. In addition, because they had anexcess of water initially, they exhibited relatively low strengthaccording to the Strength Equation. While the mixture of Example 23could be extruded, only articles of larger cross section and simpleshape were able to maintain their shape without external support. Themixtures of Examples 24-33 could be extruded within about the same rangeof pressures as the mixtures of Examples 5-9. However, the mixtures ofExamples 34-36 were unable to be extruded using the extruding equipmentavailable to the inventors.

EXAMPLES 37-53

Hydraulically settable mixtures having 4 kg of portland cement Type 1, 6kg silica sand, 50 g Tylose®, and varying amounts of water were preparedand then extruded through a die using a piston extruder. The silica sandhad a natural packing density of about 0.55 and a particle size withinthe range from about 50-80 microns. When mixed with portland cement Type1, which has a particle size within the range from about 10-25 microns,the resulting dry mixture had a particle packing density of about 0.7,which represents a better increase over the natural packing density ofeach compared to what was obtained in Examples 1-9.

The amount of water in the mixtures was varied as follows in order todetermine the extrudability of the mixture at varying levels of waterdeficiency:

    ______________________________________                                        Example       Water   % Deficient                                             ______________________________________                                        37            2.4 kg  (56.53%)                                                38            2.2 kg  (43.49%)                                                39            2.0 kg  (30.44%)                                                40            1.8 kg  (17.40%)                                                41            1.6 kg  (4.35%)                                                 42            1.4 kg  8.69%                                                   43            1.2 kg  21.73%                                                  44            1.0 kg  34.78%                                                  45            0.9 kg  41.30%                                                  46            0.8 kg  47.82%                                                  47            0.7 kg  54.34%                                                  48            0.6 kg  60.87%                                                  49            0.5 kg  67.39%                                                  50            0.4 kg  73.91%                                                  51            0.3 kg  80.43%                                                  52            0.2 kg  86.96%                                                  53            0.1 kg  93.48%                                                  ______________________________________                                    

In Examples 37-41, the number in parentheses under the heading "%Deficient" indicates the amount of excess water that was used. As above,these mixtures were "very fluid" and could not be extruded withsufficient form-stability so that an extruded object would maintain itsshape without external support. The mixtures of Examples 42-50 were ableto be extruded into a variety of form-stable articles as above,including honeycomb structures, bars, and window frames. Because of thehigher particle packing efficiencies of the mixtures of Examples 37-53compared to those of Examples 1-9, holding the water constant resultedin mixtures having decreased water deficiency and, hence, greaterflowability and lower viscosity.

As the amount of water deficiency increased, pipes of increasinglythinner walls could be extruded. In addition, the final hardenedextruded articles had higher strength compared to the articles extrudedfrom the mixtures having a lower particle packing density, whichcomports with the Strength Equation.

However, as the amount of water fell below 0.4 kg and the waterdeficiency increased to above about 75%, the mixtures could not beextruded using the equipment available, although it is believed thatusing a higher pressure extruder would make it possible, though lesspractical, to extrude such mixtures. Therefore, the mixtures in Examples51-53 could not be extruded.

From these examples it can be seen that increasing the packing densityof the solid particles while keeping the amount of added water constantresults in a mixture having less water deficiency. This allows for theextrusion of a higher packed mixture at a lower pressure for the sameamount of water.

EXAMPLES 54-67

The hydraulically settable mixtures of Examples 40-53 are repeatedexcept that silica sand having particle sizes in the range of about60-120 microns is used. The resulting particle packing density of theresulting sand and cement mixture is about 0.75. Keeping the amount ofadded water constant according to Examples 40-53 yields mixtures havingthe following amounts of water deficiency:

    ______________________________________                                        Example       Water   % Deficient                                             ______________________________________                                        54            1.8 kg  (50.94%)                                                55            1.6 kg  (34.17%)                                                56            1.4 kg  (17.40%)                                                57            1.2 kg  (0.63%)                                                 58            1.0 kg  16.14%                                                  59            0.9 kg  24.53%                                                  60            0.8 kg  32.91%                                                  61            0.7 kg  41.30%                                                  62            0.6 kg  49.69%                                                  63            0.5 kg  58.07%                                                  64            0.4 kg  66.46%                                                  65            0.3 kg  74.84%                                                  66            0.2 kg  83.23%                                                  67            0.1 kg  91.61%                                                  ______________________________________                                    

As above, keeping the amount of water constant while increasing theparticle packing density yields a hydraulically settable mixture thatcan be extruded at lower extrusion pressures. In addition, the finalhardened extruded article has higher strength according to the StrengthEquation. However, the mixtures of Examples 54-57 lack form-stabilityafter being extruded, while the mixtures of Examples 58-65 can beextruded into a number of articles, including those listed above.Finally, the mixtures of Examples 66 and 67 are too dry and viscous tobe extruded using the equipment available.

EXAMPLES 68-79

The hydraulically settable mixtures obtained in Examples 25-36 arealtered by decreasing the amount of fine silica sand to 4 kg and adding2 kg of precipitated calcium carbonate having an average particle sizeof about 1 micron. This results in a hydraulically settable mixturehaving a particle packing density of about 0.8. The resulting waterdeficiencies for a given amount of water are as follows:

    ______________________________________                                        Example       Water   % Deficient                                             ______________________________________                                        68            1.4 kg  (56.53%)                                                69            1.2 kg  (34.17%)                                                70            1.0 kg  (11.81%)                                                71            0.9 kg  (0.63%)                                                 72            0.8 kg  10.55%                                                  73            0.7 kg  21.73%                                                  74            0.6 kg  32.91%                                                  75            0.5 kg  44.10%                                                  76            0.4 kg  55.28%                                                  77            0.3 kg  66.46%                                                  78            0.2 kg  77.64%                                                  79            0.1 kg  88.82%                                                  ______________________________________                                    

As above, keeping the amount of water constant while increasing theparticle packing density yields a hydraulically settable mixture thatcan be extruded at lower extrusion pressures. In addition, the finalhardened extruded article has higher strength, according to the StrengthEquation.

EXAMPLES 80-89

The hydraulically settable mixtures obtained in Examples 44-53 arealtered by decreasing the amount of silica sand to 4 kg and adding 2 kgof precipitated calcium carbonate having an average particle size ofabout 1 micron. This results in a hydraulically settable mixture havinga particle packing density of about 0.85. The resulting waterdeficiencies for a given amount of water are as follows:

    ______________________________________                                        Example       Water   % Deficient                                             ______________________________________                                        80            1.0 kg  (58.40%)                                                81            0.9 kg  (42.56%)                                                82            0.8 kg  (26.72%)                                                83            0.7 kg  (10.88%)                                                84            0.6 kg  4.96%                                                   85            0.5 kg  20.80%                                                  86            0.4 kg  36.64%                                                  87            0.3 kg  52.48%                                                  88            0.2 kg  68.32%                                                  89            0.1 kg  84.16%                                                  ______________________________________                                    

As above, keeping the amount of water constant while increasing theparticle packing density yields a hydraulically settable mixture thatcan be extruded at lower extrusion pressures. In addition, the finalhardened extruded article has higher strength, according to the StrengthEquation.

EXAMPLES 90-95

The hydraulically settable mixtures obtained in Examples 62-67 arealtered by decreasing the amount of silica sand to 4 kg and adding 2 kgof precipitated calcium carbonate having an average particle size ofabout 1 micron. This results in a hydraulically settable mixture havinga particle packing density of about 0.9. The resulting waterdeficiencies for a given amount of water are as follows:

    ______________________________________                                        Example       Water   % Deficient                                             ______________________________________                                        90            0.6 kg  (46.06%)                                                91            0.5 kg  (21.71%)                                                92            0.4 kg  2.63%                                                   93            0.3 kg  26.97%                                                  94            0.2 kg  51.31%                                                  95            0.1 kg  75.66%                                                  ______________________________________                                    

As above, keeping the amount of water constant while increasing theparticle packing density yields a hydraulically settable mixture thatcan be extruded at lower extrusion pressures. In addition, the finalhardened extruded article has higher strength according to the StrengthEquation.

EXAMPLE 96

The procedures of Examples 1-9 are repeated, except that the averageparticle size is decreased while maintaining the same level of particlepacking density and water deficiency. The resulting hydraulicallysettable mixtures exhibit greater pseudo-plastic behavior. In otherwords, the apparent viscosities of the mixtures having a lower averageparticle size decreases for a given shear rate, while the yield stressincreases. This results in mixtures which may be extruded under lowerpressure while exhibiting greater form stability.

EXAMPLE 97

The procedures of Examples 90-95 are repeated, except that the extrudedarticles are cured by autoclaving at 400° C. and 24 bars of pressure for12 hours. The final cured articles have compressive strength of about800 MPa and a tensile strength of about 100 MPa.

EXAMPLE 98

The procedures of Examples 1-9 are repeated, except that 25 g of Tylose®4000 are added as lubricant. The resulting hydraulically settablemixtures have greater flowability and result in extruded articles havinga better surface finish. The strength properties remain approximatelythe same.

EXAMPLE 99

The procedures of Examples 1-9 are repeated, except that 25 g of calciumor magnesium stearate are added as lubricant. The resultinghydraulically settable mixtures have greater flowability and result inextruded articles having a better surface finish. The strengthproperties remain approximately the same.

EXAMPLE 100

The procedures of Examples 1-9 are repeated, except that 25 g ofpolyethylene glycol having an average molecular weight of about 35,000are added as lubricant. The resulting hydraulically settable mixtureshave greater flowability and result in extruded articles having a bettersurface finish. The strength properties remain approximately the same.

EXAMPLE 101

An extrudable hydraulically settable mixture is formed using thefollowing components:

    ______________________________________                                        Fly ash          90          g                                                Portland Cement  10          g                                                NaOH             10          g                                                Water            20          g                                                ______________________________________                                    

The sodium hydroxide raises the pH of the aqueous phase of thehydraulically settable mixture to about 14, which activates the fly ashso that it behaves as a hydraulically settable binder. Portland cementis added in order to increase the compressive strength of the finalcured product to about 20 MPa and the tensile strength to about 105 MPa.Because of the low cost of fly ash, the mixture of this example is lessexpensive than those containing higher levels of portland cement andconventional aggregates. Of course, where lower strengths areacceptable, the portland cement may be further reduced or eliminatedaltogether.

EXAMPLE 102

An extrudable hydraulically settable mixture is formed using thefollowing components:

    ______________________________________                                        Portland White Cement                                                                            4.0        kg                                              Fine Sand          6.0        kg                                              Water              1.5        kg                                              Tylose ® FL 15002                                                                            200        g                                               ______________________________________                                    

The hydraulically settable mixture is formed by mixing the ingredientstogether for 10 minutes using a high speed mixer to obtain a veryhomogeneous mixture. Thereafter, the mixture is extruded into a varietyof multi-cell structures, including "honeycomb" structures, which havevery high compressive strength, particularly in light of the open cellnature of the extruded object.

Because of the multi-cell structure, the cured material is much morelightweight than comparable solid extruded objects made from the samehydraulically settable mixtures. The block density of the multi-cellstructures is only 1.02 g/cm³. Moreover, the cured materials have acompressive strength of about 75 MPa and a tensile strength of about 28MPa. Depending upon the amount of space within the multi-cell structure,the block density can easily range anywhere from between about 0.5 g/cm³to about 1.6 g/cm³.

EXAMPLES 103-105

Extrudable hydraulically settable mixtures are formed according toExample 102, except that abaca fiber is added to the mixtures in varyingamounts as follows (measured by volume):

    ______________________________________                                        Example      Abaca Fiber                                                      ______________________________________                                        103          1%                                                               104          2%                                                               105          3%                                                               ______________________________________                                    

The resulting extruded multi-cell structures have greater strengths,both in the green state and after they are cured, than the structures ofExample 102. Moreover, the multi-cell structures formed in theseexamples are more ductile and less brittle, particularly as more fiberis added to the hydraulically settable mixture.

EXAMPLES 106-108

Extrudable hydraulically settable mixtures are formed according toExample 102, except that glass fiber is added to the mixtures in varyingamounts as follows (measured by volume):

    ______________________________________                                        Example      Glass Fiber                                                      ______________________________________                                        106          1%                                                               107          2%                                                               108          3%                                                               ______________________________________                                    

The resulting extruded multi-cell structures have greater strengths,both in the green state and after they are cured, than the structures ofExample 102. Moreover, the multi-cell structures formed in theseexamples are more ductile and less brittle, particularly as more fiberis added to the hydraulically settable mixture.

The following examples demonstrate how the strength of an extrudedhydraulically settable mixture increases or decreases as the followingvariables are varied: particle packing density, water to cement ratio,and amount of cement as a percentage of the solids content of themixture.

EXAMPLES 109-114

Extrudable hydraulically settable mixtures are formed which have 1.0 kgportland cement and 6.0 kg sand. In each mixture the portland cementcomprises 14.3% by weight of the dry mixture. The particle sizes of thesand are varied in order to yield mixtures having particle packingdensities which vary from 0.65 to 0.90 in increments of 0.05. Inaddition, the amount of water that is added is varied in order to yielda mixture having the desired level of water deficiency. In this firstset of examples, the water deficiency is 50%.

As will be shown, the compressive strength of a hydraulically settablemixture having a constant weight percentage of portland cement and sandincreases if either (1) the particle packing density is increased whilemaintaining a constant level of water deficiency or (2) the level ofwater deficiency is increased while maintaining a constant packingdensity. The amount of water is expressed in kg, while the compressivestrength is expressed in MPa. The phrase "W/C Ratio" is shorthand forwater to cement ratio.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        109    0.65         0.71     0.71    24                                       110    0.70         0.56     0.56    33                                       111    0.75         0.44     0.44    47                                       112    0.80         0.33     0.33    69                                       113    0.85         0.23     0.23    103                                      114    0.90         0.15     0.15    160                                      ______________________________________                                    

These examples clearly demonstrate that the strength of an extrudedarticle will greatly increase as the particle packing density isincreased, even while the absolute level of cement and sand are heldconstant. This correlates to the Strength Equation because as theparticle packing density is increased both the amount of air and waterwithin the mixture are decreased. However, because the amount of waterdeficiency is held constant, the mixtures have similar levels ofworkability and may be extruded using similar extrusion pressures. Thestrengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 8A.

EXAMPLES 115-120

The compositions of Examples 109-114 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        115    0.65         0.57     0.57    31                                       116    0.70         0.45     0.45    43                                       117    0.75         0.35     0.35    59                                       118    0.80         0.26     0.26    84                                       119    0.85         0.19     0.19    121                                      120    0.90         0.12     0.12    182                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 8B.

EXAMPLES 121-126

The compositions of Examples 109-114 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        121    0.65         0.42     0.42     42                                      122    0.70         0.34     0.34     57                                      123    0.75         0.26     0.26     76                                      124    0.80         0.20     0.20    105                                      125    0.85         0.14     0.14    146                                      126    0.90         0.09     0.09    209                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 8C.

EXAMPLES 127-132

The compositions of Examples 109-114 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        127    0.65         0.28     0.28     60                                      128    0.70         0.23     0.23     78                                      129    0.75         0.18     0.18    102                                      130    0.80         0.13     0.13    134                                      131    0.85         0.09     0.09    179                                      132    0.90         0.06     0.06    243                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 8D.

EXAMPLES 133-138

The compositions of Examples 109-114 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        133    0.65         0.14     0.14     94                                      134    0.70         0.11     0.11    116                                      135    0.75         0.09     0.09    143                                      136    0.80         0.07     0.07    179                                      137    0.85         0.05     0.05    224                                      138    0.90         0.03     0.03    285                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 8E.Superimposing the curves of FIGS. 8A-8E yields substantially onecontinuous curve, which demonstrates the close relationship betweenstrength and the absolute level of water within the hydraulicallysettable mixture. This clearly demonstrates that in order tosimultaneously achieve high strength and high workability in a givenmixture, it is advantageous to increase the particle packing densityrather than increase the level of water in order to increase theflowability of the mixture under pressure.

The next set of examples is substantially similar to Examples 109-138,except that the amount of portland cement is increased to 25% by weightof the dry mixtures. The purpose of these examples is to demonstratethat only modest increases of strength are attained by increasing theamount of hydraulically settable binder, while the most dramaticincreases in strength are achieved by increasing the particle packingdensity and decreasing the amount of water within the mixtures.

EXAMPLES 139-144

Extrudable hydraulically settable mixtures are formed which have 2.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        139    0.65         0.79     0.40     52                                      140    0.70         0.63     0.32     69                                      141    0.75         0.49     0.25     90                                      142    0.80         0.37     0.18    120                                      143    0.85         0.26     0.13    160                                      144    0.90         0.16     0.08    215                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 9A.

EXAMPLES 145-150

The compositions of Examples 138-139 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        145    0.65         0.63     0.32     65                                      146    0.70         0.50     0.25     83                                      147    0.75         0.39     0.20    107                                      148    0.80         0.29     0.15    138                                      149    0.85         0.21     0.10    179                                      150    0.90         0.13     0.07    234                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 9B.

EXAMPLES 151-156

The compositions of Examples 138-139 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        151    0.65         0.48     0.24     82                                      152    0.70         0.38     0.19    103                                      153    0.75         0.29     0.15    129                                      154    0.80         0.22     0.11    162                                      155    0.85         0.16     0.08    203                                      156    0.90         0.10     0.05    255                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 9C.

EXAMPLES 157-162

The compositions of Examples 138-139 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        157    0.65         0.32     0.16    109                                      158    0.70         0.25     0.13    132                                      159    0.75         0.20     0.10    159                                      160    0.80         0.15     0.07    192                                      161    0.85         0.10     0.05    231                                      162    0.90         0.07     0.03    279                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 9D.

EXAMPLES 163-168

The compositions of Examples 138-139 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        163    0.65         0.16     0.08    150                                      164    0.70         0.13     0.06    173                                      165    0.75         0.10     0.05    200                                      166    0.80         0.07     0.04    231                                      167    0.85         0.05     0.03    267                                      168    0.90         0.03     0.02    308                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 9E.Superimposing the curves of FIGS. 9A-9E yields substantially onecontinuous curve, which demonstrates the close relationship betweenstrength and the absolute level of water within the hydraulicallysettable mixture. Although increasing the amount of portland cementwithin the mixtures of Examples 139-168 causes an increase in theoverall strength of the mixtures, the increase is less dramatic thanincreasing the particle packing density and decreasing the level ofwater within the mixtures.

The next set of examples is substantially similar to Examples 139-168,except that the amount of portland cement is increased to 33% by weightof the dry mixtures.

EXAMPLES 169-174

Extrudable hydraulically settable mixtures are formed which have 3.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        169    0.65         0.88     0.29     74                                      170    0.70         0.70     0.23     94                                      171    0.75         0.54     0.18    118                                      172    0.80         0.41     0.14    150                                      173    0.85         0.29     0.10    189                                      174    0.90         0.18     0.06    240                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 10A.

EXAMPLES 175-180

The compositions of Examples 169-174 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        175    0.65         0.70     0.23     89                                      176    0.70         0.56     0.19    111                                      177    0.75         0.43     0.14    137                                      178    0.80         0.33     0.11    169                                      179    0.85         0.23     0.08    208                                      180    0.90         0.14     0.05    256                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 10B.

EXAMPLES 181-186

The compositions of Examples 169-174 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        181    0.65         0.53     0.18    109                                      182    0.70         0.42     0.14    133                                      183    0.75         0.33     0.11    160                                      184    0.80         0.24     0.08    192                                      185    0.85         0.17     0.06    229                                      186    0.90         0.11     0.04    274                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 10C.

EXAMPLES 187-192

The compositions of Examples 169-174 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        187    0.65         0.35     0.12    138                                      188    0.70         0.28     0.09    162                                      189    0.75         0.22     0.07    189                                      190    0.80         0.16     0.05    220                                      191    0.85         0.12     0.04    254                                      192    0.90         0.07     0.02    294                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 10D.

EXAMPLES 193-198

The compositions of Examples 169-174 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        193    0.65         0.18     0.06    180                                      194    0.70         0.14     0.05    203                                      195    0.75         0.11     0.04    227                                      196    0.80         0.08     0.03    254                                      197    0.85         0.06     0.02    283                                      198    0.90         0.04     0.01    316                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 10E.Superimposing the curves of FIGS. 10A-10E yields substantially onecontinuous curve, which demonstrates the close relationship betweenstrength and the absolute level of water within the hydraulicallysettable mixture. Although increasing the amount of portland cementwithin the mixtures of Examples 169-198 causes an increase in theoverall strength of the mixtures, the increase is less dramatic thanincreasing the particle packing density and decreasing the level ofwater within the mixtures.

The next set of examples is substantially similar to Examples 169-198,except that the amount of portland cement is increased to 40% by weightof the dry mixtures.

EXAMPLES 199-204

Extrudable hydraulically settable mixtures are formed which have 4.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        199    0.65         0.96     0.24     90                                      200    0.70         0.77     0.19    111                                      201    0.75         0.60     0.15    138                                      202    0.80         0.45     0.11    169                                      203    0.85         0.32     0.08    208                                      204    0.90         0.20     0.05    254                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 11A.

EXAMPLES 205-210

The compositions of Examples 199-204 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        205    0.65         0.77     0.19    106                                      206    0.70         0.61     0.15    129                                      207    0.75         0.48     0.12    156                                      208    0.80         0.36     0.09    188                                      209    0.85         0.25     0.06    225                                      210    0.90         0.16     0.04    269                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 11B.

EXAMPLES 211-216

The compositions of Examples 199-204 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        211    0.65         0.58     0.14    128                                      212    0.70         0.46     0.11    152                                      213    0.75         0.36     0.09    179                                      214    0.80         0.27     0.07    210                                      215    0.85         0.19     0.05    245                                      216    0.90         0.12     0.03    284                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 11C.

EXAMPLES 217-222

The compositions of Examples 199-204 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        217    0.65         0.39     0.10    158                                      218    0.70         0.31     0.08    181                                      219    0.75         0.24     0.06    207                                      220    0.80         0.18     0.04    236                                      221    0.85         0.13     0.03    267                                      222    0.90         0.08     0.02    301                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 11D.

EXAMPLES 223-228

The compositions of Examples 199-204 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        223    0.65         0.19     0.05    199                                      224    0.70         0.15     0.04    220                                      225    0.75         0.12     0.03    243                                      226    0.80         0.09     0.02    267                                      227    0.85         0.06     0.02    292                                      228    0.90         0.04     0.01    320                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 11E.Superimposing the curves of FIGS. 11A-11E yields substantially onecontinuous curve, which demonstrates the close relationship betweenstrength and the absolute level of water within the hydraulicallysettable mixture. Although increasing the amount of portland cementwithin the mixtures of Examples 199-228 causes an increase in theoverall strength of the mixtures, the increase is less dramatic thanincreasing the particle packing density and decreasing the level ofwater within the mixtures.

The next set of examples is substantially similar to Examples 199-228,except that the amount of portland cement is increased to 45.5% byweight of the dry mixtures.

EXAMPLES 229-234

Extrudable hydraulically settable mixtures are formed which have 5.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        229    0.65         1.05     0.21    102                                      230    0.70         0.83     0.17    125                                      231    0.75         0.65     0.13    152                                      232    0.80         0.49     0.10    183                                      233    0.85         0.34     0.07    220                                      234    0.90         0.22     0.04    263                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 12A.

EXAMPLES 235-240

The compositions of Examples 229-234 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        235    0.65         0.84     0.17    120                                      236    0.70         0.67     0.13    143                                      237    0.75         0.52     0.10    170                                      238    0.80         0.39     0.08    201                                      239    0.85         0.27     0.05    236                                      240    0.90         0.17     0.03    276                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 12B.

EXAMPLES 241-246

The compositions of Examples 229-234 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        241    0.65         0.63     0.13    142                                      242    0.70         0.50     0.10    166                                      243    0.75         0.39     0.08    193                                      244    0.80         0.29     0.06    222                                      245    0.85         0.21     0.04    254                                      246    0.90         0.13     0.03    291                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 12C.

EXAMPLES 247-252

The compositions of Examples 229-234 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        247    0.65         0.42     0.08    172                                      248    0.70         0.33     0.07    195                                      249    0.75         0.26     0.05    220                                      250    0.80         0.19     0.04    246                                      251    0.85         0.14     0.03    275                                      252    0.90         0.09     0.02    306                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 12D.

EXAMPLES 253-258

The compositions of Examples 229-234 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        253    0.65         0.21     0.04    211                                      254    0.70         0.17     0.03    232                                      255    0.75         0.13     0.03    253                                      256    0.80         0.10     0.02    275                                      257    0.85         0.07     0.01    298                                      258    0.90         0.04     0.01    322                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 12E.Superimposing the curves of FIGS. 12A-12E yields substantially onecontinuous curve, which demonstrates the close relationship betweenstrength and the absolute level of water within the hydraulicallysettable mixture. Although increasing the amount of portland cementwithin the mixtures of Examples 229-258 causes an increase in theoverall strength of the mixtures, the increase is less dramatic thanincreasing the particle packing density and decreasing the level ofwater within the mixtures.

The next set of examples is substantially similar to Examples 229-258,except that the amount of portland cement is increased to 50% by weightof the dry mixtures.

EXAMPLES 259-264

Extrudable hydraulically settable mixtures are formed which have 6.0 kgportland cement and 6.0 kg sand. The particle sizes of the sand arevaried in order to yield mixtures having particle packing densitieswhich vary from 0.65 to 0.90 in increments of 0.05. In addition, theamount of water that is added is varied in order to yield a mixturehaving the desired level of water deficiency. In this first set ofexamples, the water deficiency is 50%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        259    0.65         1.13     0.19    112                                      260    0.70         0.90     0.15    135                                      261    0.75         0.70     0.12    162                                      262    0.80         0.53     0.09    193                                      263    0.85         0.37     0.06    229                                      264    0.90         0.23     0.04    270                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 13A.

EXAMPLES 265-270

The compositions of Examples 259-264 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 60%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        265    0.65         0.91     0.15    130                                      266    0.70         0.72     0.12    154                                      267    0.75         0.56     0.09    181                                      268    0.80         0.42     0.07    211                                      269    0.85         0.30     0.05    244                                      270    0.90         0.19     0.03    282                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 13B.

EXAMPLES 271-276

The compositions of Examples 259-264 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 70%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        271    0.65         0.68     0.11    153                                      272    0.70         0.54     0.09    176                                      273    0.75         0.42     0.07    202                                      274    0.80         0.32     0.05    231                                      275    0.85         0.22     0.04    261                                      276    0.90         0.14     0.02    295                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 13C.

EXAMPLES 277-282

The compositions of Examples 259-264 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 80%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        277    0.65         0.45     0.08    182                                      278    0.70         0.36     0.06    204                                      279    0.75         0.28     0.05    228                                      280    0.80         0.21     0.04    254                                      281    0.85         0.15     0.02    280                                      282    0.90         0.09     0.02    309                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 13D.

EXAMPLES 283-288

The compositions of Examples 259-264 are substantially repeated exceptthat the amount of water is reduced in each example in order to yield awater deficiency of 90%.

    ______________________________________                                        Example                                                                              Packing Density                                                                            Water    W/C Ratio                                                                             Strength                                 ______________________________________                                        283    0.65         0.23     0.04    221                                      284    0.70         0.18     0.03    240                                      285    0.75         0.14     0.02    260                                      286    0.80         0.11     0.02    280                                      287    0.85         0.07     0.01    302                                      288    0.90         0.05     0.01    324                                      ______________________________________                                    

The strengths of the different compositions as a function of particlepacking are plotted and illustrated by the graph of FIG. 13E.Superimposing the curves of FIGS. 13A-13E yields substantially onecontinuous curve, which demonstrates the close relationship betweenstrength and the absolute level of water within the hydraulicallysettable mixture. Although increasing the amount of portland cementwithin the mixtures of Examples 259-288 causes an increase in theoverall strength of the mixtures, the increase is less dramatic thanincreasing the particle packing density and decreasing the level ofwater within the mixtures.

The next group of examples illustrates how the overall particle packingdensity of a two-component system (i.e., portland cement and sand) isaffected by the natural packing densities of the sand component and theportland cement component. Using the information contained in theseexamples would allow one of ordinary skill in the art to designhydraulically settable mixtures having the particle packing densities ofthe compositions set forth above in Examples 109-288. As shown below,the resulting particle packing density is affected not only by theindividual natural packing densities for the cement and sand componentsbut also by the average particle diameter of the cement and sandcomponents, respectively.

Note that different sand aggregates may have the same average diameterand yet have greatly varying packing densities. The natural packingdensity of an aggregate of a given average diameter will increase ordecrease depending on the distribution of particle diameters away fromthe mean diameter. In general, the greater the size variation among theparticles the greater the natural packing density of a given aggregate.

EXAMPLES 289-294

Hydraulically settable mixtures are formed which contain 1.0 kg portlandcement and 6.0 kg sand, yielding mixtures having 14.3% cement and 85.7%sand aggregate by weight of the dry components. The portland cement hasan average particle size of 15 microns and a natural packing density of0.580. Five different types of sand aggregate categorized on the basisof average diameter are selected to yield the desired overall packingdensity of the dry mixture. The five different aggregates, which shallbe referred to as "Aggregate 1", "Aggregate 2" and so on, have averageparticle diameters of 0.1 mm, 0.2 mm, 0.5 mm, 1.0 mm, and 1.25 mm,respectively.

Each of the five types of sand aggregate is further distinguished on thebasis of natural packing density, as set forth below. The followingtable illustrates the effect on the overall particle packing density ofmixing the five different types of aggregates having varying particlepacking densities with the portland cement described above. The term"Aggregate" is abbreviated as "Agg"; the overall packing density isabbreviated as "Density"; and the numbers below each of the Aggregateheadings is the natural packing density for a given aggregate.

    ______________________________________                                        Example                                                                              Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                               ______________________________________                                        289    0.65     0.595   0.586 0.579 0.577 0.577                               290    0.70     0.644   0.633 0.623 0.622 0.622                               291    0.75     0.696   0.682 0.673 0.670 0.669                               292    0.80     0.755   0.738 0.726 0.722 0.722                               293    0.85     0.828   0.806 0.791 0.786 0.785                               294    0.90     N/A     0.945 0.918 0.907 0.905                               ______________________________________                                    

As illustrated by these examples, greater overall particle packingdensity can be achieved either by keeping the average diameter of theaggregate constant while increasing the natural packing density of theaggregate, or by keeping the natural packing density constant andincreasing the average diameter of the aggregate. The increased packingeffect using the latter method is caused by the increase in variancebetween the average aggregate particle size and cement particle size.However, varying the natural packing density of a given aggregateappears to yield the greater increase in overall packing density.

EXAMPLES 295-298

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 2.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 25% cement and sand aggregate byweight of the dry components. The average particle size of the portlandcement and the five different sand aggregate types of the followingexamples are the same as in Examples 289-294.

    ______________________________________                                        Example                                                                              Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                               ______________________________________                                        295    0.65     0.554   0.536 0.524 0.521 0.520                               296    0.70     0.612   0.589 0.575 0.570 0.569                               297    0.75     0.683   0.654 0.635 0.628 0.627                               298    0.80     0.785   0.745 0.718 0.708 0.707                               ______________________________________                                    

As illustrated in these examples, as the quantity of portland cement isincreased, the difficulty of creating mixtures from a two-componentsystem which have high overall packing density also increases. This isbecause of the general uniformity of particle sizes of the portlandcement compared to the sand aggregate. Greater particle uniformitygenerally decreases the ability to achieve higher particle packingdensities.

EXAMPLES 299-302

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 3.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 33.3% cement and 66.7% sandaggregate by weight of the dry components. The average particle size ofthe portland cement and the five different sand aggregate types of thefollowing examples are the same as in Examples 289-294.

    ______________________________________                                        Example                                                                              Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                               ______________________________________                                        299    0.65     0.529   0.502 0.488 0.483 0.482                               300    0.70     0.601   0.568 0.547 0.540 0.538                               301    0.75     0.709   0.661 0.629 0.618 0.616                               302    0.80     0.950   0.915 0.849 0.816 0.809                               ______________________________________                                    

EXAMPLES 303-305

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 4.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 40% cement and sand aggregate byweight of the dry components. The average particle size of the portlandcement and the five different sand aggregate types of the followingexamples are the same as in Examples 289-294.

    ______________________________________                                        Example                                                                              Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                               ______________________________________                                        303    0.65     0.515   0.483 0.462 0.456 0.454                               304    0.70     0.609   0.562 0.533 0.523 0.522                               305    0.75     0.792   0.719 0.662 0.643 0.639                               ______________________________________                                    

EXAMPLES 306-308

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 5.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 45.5% cement and 54.5% sandaggregate by weight of the dry components. The average particle size ofthe portland cement and the five different sand aggregate types of thefollowing examples are the same as in Examples 289-294.

    ______________________________________                                        Example                                                                              Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                               ______________________________________                                        306    0.65     0.508   0.468 0.444 0.435 0.434                               307    0.70     0.634   0.571 0.531 0.518 0.515                               308    0.75     N/A     N/A   0.894 0.835 0.819                               ______________________________________                                    

EXAMPLES 309-310

The compositions, methodologies, and assumptions set forth in Examples289-294 are repeated in every way, except that the hydraulicallysettable mixtures contain 6.0 kg portland cement and 6.0 kg of sandaggregate, yielding mixtures having 50% cement and sand aggregate byweight of the dry components. The average particle size of the portlandcement and the five different sand aggregate types of the followingexamples are the same as in Examples 289-294.

    ______________________________________                                        Example                                                                              Density  Agg 1   Agg 2 Agg 3 Agg 4 Agg 5                               ______________________________________                                        309    0.65     0.507   0.459 0.430 0.421 0.419                               310    0.70     0.682   0.599 0.543 0.525 0.521                               ______________________________________                                    

IV. SUMMARY

From the foregoing, it will be appreciated that the present inventionprovides novel compositions and methods for making a variety of extrudedhydraulically settable articles of manufacture which have heretofore notbeen possible.

In particular, the present invention provides novel compositions andmethods for improving the extrudability of hydraulically settablematerials. Specifically, the present invention allows for the formationof extruded products and shapes which have not heretofore been possibleusing traditional hydraulic materials because of the inherent strengthand moldability limitations of presently known hydraulically settablecompositions.

In addition, the present invention provides novel compositions andmethods which result in the ability to extrude hydraulically settableproducts having excellent form-stability in the green state. Suchextruded objects have the benefit of being immediately self-supportingwithout external support even before they have cured.

Further, the present invention provides novel compositions and processeswhich yield highly plastic compositions which will maintain whatevershape into which the are extruded. Such extruded objects can usually behandled and transported using conventional means shortly after beingextruded.

The present invention further provides novel compositions and processeswhich yield a variety of thin-walled extruded objects, which are oftenmore lightweight and less dense than presently known hydraulicallysettable materials. Such extruded hydraulically settable products alsoshow an increase in strength without a corresponding increase indensity.

The present invention further provides novel compositions and processesuseful for extruding hydraulically settable objects that can take theplace of products which are presently made from other materials, such aspaper, paperboard, plastic polystyrene, or metal. A further advantage isthat such hydraulically settable products can be made to have similar,or even superior, properties than those presently made from existingmaterials.

In addition, the present invention provides novel compositions andprocesses which yield hydraulically settable objects that areenvironmentally benign and which essentially consist of the componentsfound naturally within the earth into which such materials mighteventually be disposed. Finally, the present invention provides novelcompositions and processes for extruding hydraulically settable objectsat a cost that is comparable, or even superior, to the cost ofmanufacturing equivalent objects from paper, paperboard, plastic,polystyrene, or metal.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed and desired to be secured by U.S. Letters Patent is: 1.A method for extruding a hydraulically settable mixture to form anarticle of manufacture having a hydraulically settable matrix, themethod comprising the steps of:combining a hydraulically settablebinder, at least one aggregate material, a rheology-modifying agent andwater to form a hydraulically settable mixture, the hydraulicallysettable binder and at least one aggregate material each comprising aplurality of particles which form a combination of particles that are inan initial state of natural packing density, the hydraulically settablemixture having an initial net deficiency of water such that the mixtureis initially granular and substantially noncohesive; extruding thehydraulically settable mixture under an extrusion pressure sufficient toincrease the initial packing density of the combination of thehydraulically settable binder particles and aggregate materialparticles, thereby reducing the initial net deficiency of water, causingthe hydraulically settable mixture to become cohesive, and causing themixture to flow through a die to form an extruded article of manufactureof a desired shape and having a hydraulically settable matrix, thehydraulically settable matrix of the extruded article of manufacturebeing form-stable immediately after being extruded through the die; andallowing the hydraulically settable matrix of the extruded article ofmanufacture to cure.
 2. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the natural packing density ofthe combination of hydraulically settable particles and aggregatematerial particles is in a range from about 0.65 to about 0.99.
 3. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the natural packing density of the combination ofhydraulically settable particles and aggregate material particles is ina range from about 0.7 to about 0.95.
 4. A method for extruding ahydraulically settable mixture as defined in claim 1, wherein thenatural packing density of the combination of hydraulically settableparticles and aggregate material particles is in a range from about 0.75to about 0.9.
 5. A method for extruding a hydraulically settable mixtureas defined in claim 1, wherein the combining step includes mixing usinga high shear mixer.
 6. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the extruding step is carried outusing an auger extruder.
 7. A method for extruding a hydraulicallysettable mixture as defined in claim 6, wherein the extruding stepincludes applying a negative pressure to the hydraulically settablemixture in order to remove air from the mixture.
 8. A method forextruding a hydraulically settable mixture as defined in claim 1,wherein the extruding step is carried out using a piston extruder.
 9. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the extrusion pressure is in a range from about 10 barsto about 7000 bars.
 10. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the extrusion pressure is in arange from about 20 bars to about 3000 bars.
 11. A method for extrudinga hydraulically settable mixture as defined in claim 1, wherein theextrusion pressure is in a range from about 50 bars to about 200 bars.12. A method for extruding a hydraulically settable mixture as definedin claim 1, wherein the hydraulically settable binder compriseshydraulic cement.
 13. A method for extruding a hydraulically settablemixture as defined in claim 12, wherein the hydraulic cement includesportland cement.
 14. A method for extruding a hydraulically settablemixture as defined in claim 12, wherein the hydraulic cement includes acement selected from the group consisting of microfine cement, slagcement, calcium aluminate cement, plaster, silicate cement, gypsumcement, phosphate cement, white cement, high-alumina cement, magnesiumoxychloride cement, aggregates coated with microfine cement particles,and mixtures thereof.
 15. A method for extruding a hydraulicallysettable mixture as defined in claim 12, wherein the hydraulic cementincludes a cement selected from the group consisting of macro defectfree cement and DSP cement.
 16. A method for extruding a hydraulicallysettable mixture as defined in claim 1, wherein the hydraulicallysettable binder comprises gypsum hemihydrate.
 17. A method for extrudinga hydraulically settable mixture as defined in claim 1, wherein thehydraulically settable binder comprises fly ash activated with a strongbase.
 18. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the combining step includes adding a fibrousmaterial to the hydraulically settable mixture.
 19. A method forextruding a hydraulically settable mixture as defined in claim 18,wherein the fibrous material comprises cellulosic fibers.
 20. A methodfor extruding a hydraulically settable mixture as defined in claim 19,wherein the cellulosic fibers are selected from the group consisting ofcotton, bagasse, hemp, abaca, sisal, and mixtures thereof.
 21. A methodfor extruding a hydraulically settable mixture as defined in claim 19,wherein the cellulosic fibers comprise wood fibers.
 22. A method forextruding a hydraulically settable mixture as defined in claim 18,wherein the fibrous material is selected from the group consisting ofceramic fibers, glass fibers, carbon fibers, and mixtures thereof.
 23. Amethod for extruding a hydraulically settable mixture as defined inclaim 18, wherein the fibrous material comprises metal fibers.
 24. Amethod for extruding a hydraulically settable mixture as defined inclaim 18, wherein the fibrous material comprises synthetic organicpolymer fibers.
 25. A method for extruding a hydraulically settablemixture as defined in claim 18, wherein the fibrous material has aconcentration in a range from about 0.5% to about 30% by volume of thehydraulically settable mixture.
 26. A method for extruding ahydraulically settable mixture as defined in claim 18, wherein thefibrous material has a concentration in a range from about 1% to about20% by volume of the hydraulically settable mixture.
 27. A method forextruding a hydraulically settable mixture as defined in claim 18,wherein the fibrous material has a concentration in a range from about2% to about 10% by volume of the hydraulically settable mixture.
 28. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the step of allowing the hydraulically settable matrixto cure includes autoclaving the extruded article of manufacture.
 29. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the step of allowing the hydraulically settable matrixto cure includes passing the extruded article by a source of thermalenergy.
 30. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the rheology-modifying agent is included ina range from about 0.1% to about 5% by weight of the hydraulicallysettable mixture exclusive of the water.
 31. A method for extruding ahydraulically settable mixture as defined in claim 1, wherein therheology-modifying agent is included in a range from about 0.5% to about1% by weight of the hydraulically settable mixture exclusive of thewater.
 32. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the rheology-modifying agent comprises acellulose-based material or a derivative thereof.
 33. A method forextruding a hydraulically settable mixture as defined in claim 32,wherein the cellulose-based material is selected from the groupconsisting of methylhydroxyethylcellulose, hydroxymethylethylcellulose,carboxymethylcellulose, methylcellulose, ethylcellulose,hydroxyethylcellulose, hydroxyethylpropylcellulose, and mixturesthereof.
 34. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the rheology-modifying agent comprises astarch-based material or a derivative thereof.
 35. A method forextruding a hydraulically settable mixture as defined in claim 34,wherein the starch-based material is selected from the group consistingof amylopectin, amylose, sea gel, starch acetates, starch hydroxyethylethers, ionic starches, long-chain alkyl starches, dextrins, aminestarches, phosphate starches, dialdehyde starches, and mixtures thereof.36. A method for extruding a hydraulically settable mixture as definedin claim 1, wherein the rheology-modifying agent comprises aprotein-based material or a derivative thereof.
 37. A method forextruding a hydraulically settable mixture as defined in claim 36,wherein the protein-based material is selected from the group consistingof prolamine, collagen derivatives, gelatin, glue, casein, and mixturesthereof.
 38. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the rheology-modifying agent comprises asynthetic organic material.
 39. A method for extruding a hydraulicallysettable mixture as defined in claim 38, wherein the synthetic organicmaterial is selected from the group consisting of polyvinyl pyrrolidone,polyethylene glycol, polyvinyl alcohol, polyvinylmethyl ether,polyacrylic acids, polyacrylic acid salts, polyvinylacrylic acids,polyvinylacrylic acid salts, polylactic acid, polyacrylimides, ethyleneoxide polymers, latex, and mixtures thereof.
 40. A method for extrudinga hydraulically settable mixture as defined in claim 1, wherein therheology-modifying agent is selected from the group consisting ofalginic acid, phycocolloids, agar, gum arabic, guar gum, locust beangum, gum karaya, gum tragacanth, and mixtures thereof.
 41. A method forextruding a hydraulically settable mixture as defined in claim 1,wherein the combining step includes adding a dispersant to thehydraulically settable mixture.
 42. A method for extruding ahydraulically settable mixture as defined in claim 41, wherein thedispersant is combined into the hydraulically settable mixture after theformation of early hydration products.
 43. A method for extruding ahydraulically settable mixture as defined in claim 41, wherein thedispersant is selected from the group consisting of sulfonatednaphthalene-formaldehyde condensate, sulfonated melamineformaldehydecondensate, lignosulfonate, acrylic acid, and salts of the foregoing.44. A method for extruding a hydraulically settable mixture as definedin claim 41, wherein the dispersant is added to the hydraulicallysettable mixture prior to adding the rheology-modifying agent to themixture.
 45. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the aggregate material includes clay.
 46. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the aggregate material is selected from the groupconsisting of gravel, sand, alumina, silica sand, fused silica, crushedlimestone, crushed sandstone, crushed granite, crushed basalt, andmixtures thereof.
 47. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the aggregate material includessilica fume.
 48. A method for extruding a hydraulically settable mixtureas defined in claim 1, wherein the aggregate material includeshydraulically settable binder particles that are at least partiallyhydrated.
 49. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the aggregate material includes fly ash. 50.A method for extruding a hydraulically settable mixture as defined inclaim 1, further including the step of joining together a plurality ofextruded articles of manufacture.
 51. A method for extruding ahydraulically settable mixture as defined in claim 1, further includingthe step of reshaping the extruded article of manufacture into a desiredshape.
 52. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the extruding step includes extruding thehydraulically settable mixture into a pipe.
 53. A method for extruding ahydraulically settable mixture as defined in claim 1, wherein theextruding step includes extruding the hydraulically settable mixtureinto a bar.
 54. A method for extruding a hydraulically settable mixtureas defined in claim 1, wherein the extruding step includes extruding thehydraulically settable mixture into a multicellular structure.
 55. Amethod for extruding a hydraulically settable mixture as defined inclaim 54, wherein the multicellular structure comprises a honeycombstructure.
 56. A method for extruding a hydraulically settable mixtureas defined in claim 54, wherein the multicellular structure has a bulkdensity up to about 1.5 g/cm³.
 57. A method for extruding ahydraulically settable mixture as defined in claim 54, wherein themulticellular structure has a bulk density up to about 0.7 g/cm³.
 58. Amethod for extruding a hydraulically settable mixture as defined inclaim 54, wherein the multicellular structure has a bulk density up toabout 0.3 g/cm³.
 59. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the extruding step includesextruding the hydraulically settable mixture into an I-beam.
 60. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the extruding step includes extruding the hydraulicallysettable mixture into a sheet.
 61. A method for extruding ahydraulically settable mixture as defined in claim 1, wherein theextruding step includes extruding the hydraulically settable mixtureinto a board.
 62. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the extruding step includesextruding the hydraulically settable mixture into a two-by-four.
 63. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the extruding step includes extruding the hydraulicallysettable mixture into a window frame.
 64. A method for extruding ahydraulically settable mixture as defined in claim 1, wherein theextruding step includes extruding the hydraulically settable mixtureinto a brick.
 65. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the extruding step includesextruding the hydraulically settable mixture into a roofing tile.
 66. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the extruding step includes extruding the hydraulicallysettable mixture into a wall panel.
 67. A method for extruding ahydraulically settable mixture as defined in claim 1, wherein thehydraulically settable matrix has a thickness less than about 3 min. 68.A method for extruding a hydraulically settable mixture as defined inclaim 1, wherein the hydraulically settable matrix has a thickness lessthan about 1 mm.
 69. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the hydraulically settable matrixincludes a wall having a thickness and defining a cavity, and whereinthe wall thickness to cavity ratio of the hydraulically settable matrixis less than about 0.25.
 70. A method for extruding a hydraulicallysettable mixture as defined in claim 69, wherein the wall thickness tocavity ratio of the hydraulically settable matrix is less than about0.15.
 71. A method for extruding a hydraulically settable mixture asdefined in claim 69, wherein the wall thickness to cavity ratio of thehydraulically settable matrix is less than about 0.1.
 72. A method forextruding a hydraulically settable mixture as defined in claim 1,wherein the cured hydraulically settable matrix of the article ofmanufacture has a tensile strength greater than about 15 MPa.
 73. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the cured hydraulically settable matrix of the articleof manufacture has a tensile strength greater than about 30 MPa.
 74. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the cured hydraulically settable matrix of the articleof manufacture has a tensile strength greater than about 50 MPa.
 75. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the cured hydraulically settable matrix has a tensilestrength to bulk density ratio greater than about 5 MPa·cm³ /g.
 76. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the cured hydraulically settable matrix has a tensilestrength to bulk density ratio greater than about 15 MPa·cm³ /g.
 77. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the cured hydraulically settable matrix has a tensilestrength to bulk density ratio greater than about 30 MPa·cm³ /g.
 78. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the hydraulically settable binder and water togetherform a hydraulic paste having a specific gravity greater than about 2.2.79. A method for extruding a hydraulically settable mixture as definedin claim 1, wherein the hydraulically settable binder and water togetherform a hydraulic paste having a specific gravity greater than about 2.5.80. A method for extruding a hydraulically settable mixture as definedin claim 1, wherein the hydraulically settable binder and water togetherform a hydraulic paste having a specific gravity greater than about 2.7.81. A method for extruding a hydraulically settable mixture as definedin claim 1, wherein the hydraulically settable mixture has a water tohydraulically settable binder ratio less than about 0.35 w/w.
 82. Amethod for extruding a hydraulically settable mixture as defined inclaim 1, wherein the initial net deficiency of water is at least about10%.
 83. A method for extruding a hydraulically settable mixture asdefined in claim 1, wherein the initial net deficiency of water is atleast about 25%.
 84. A method for extruding a hydraulically settablemixture as defined in claim 1, wherein the initial net deficiency ofwater is at least about 50%.
 85. A method for extruding a hydraulicallysettable mixture as defined in claim 1, wherein the initial netdeficiency of water is at least about 75%.
 86. A method for extruding ahydraulically settable mixture to form an article of manufacture havinga hydraulically settable matrix, the method including the stepsof:mixing a hydraulically settable binder, at least one aggregatematerial, and water under sufficient shear to create a substantiallyhomogeneous hydraulically settable mixture having an initial netdeficiency of water such that the mixture is initially granular andsubstantially noncohesive; extruding the hydraulically settable mixtureunder a pressure sufficient to cause the mixture to become cohesive andflow through a die to form an article of manufacture of a desired shapeand having a hydraulically settable matrix, the hydraulically settablematrix of the extruded article of manufacture being form-stableimmediately after being extruded through the die, the hydraulicallysettable matrix including a wall having a thickness and defining acavity, the wall thickness to cavity ratio of the hydraulically settablematrix being less than about 0.25; and allowing the hydraulicallysettable matrix of the extruded article of manufacture to cure.
 87. Amethod for extruding a hydraulically settable mixture as defined inclaim 86, wherein the wall thickness to cavity ratio of thehydraulically settable matrix is less than about 0.15.
 88. A method forextruding a hydraulically settable mixture as defined in claim 86,wherein the wall thickness to cavity ratio of the hydraulically settablematrix is less than about 0.1.
 89. A method for extruding ahydraulically settable mixture to form an article of manufacture havinga hydraulically settable matrix, the method including the stepsof:combining a hydraulically settable binder, at least one aggregatematerial, and water to form a hydraulically settable mixture having aninitial net deficiency of water such that the mixture is initiallygranular and substantially noncohesive; extruding the hydraulicallysettable mixture under a pressure sufficient to cause the mixture tobecome cohesive and flow through a die to form an article of manufactureof a desired shape and having a hydraulically settable matrix, thehydraulically settable matrix of the extruded article of manufacturebeing form-stable immediately after being extruded through the die; andallowing the hydraulically settable matrix of the extruded article ofmanufacture to cure, wherein the cured hydraulically settable matrix ofthe article of manufacture has a bulk density less than about 1.5 g/cm³.90. A method for extruding a hydraulically settable mixture to form anarticle of manufacture having a hydraulically settable matrix, themethod including the steps of:mixing a hydraulically settable binder, atleast one aggregate material, and water under sufficient shear to createa substantially homogeneous hydraulically settable mixture having aninitial net deficiency of water such that the mixture is initiallygranular and substantially noncohesive; extruding the hydraulicallysettable mixture under a pressure sufficient to cause the mixture tobecome cohesive and flow through a die to form an article of manufactureof a desired shape and having a hydraulically settable matrix, thehydraulically settable matrix of the extruded article of manufacturebeing form-stable immediately after being extruded through the die; andallowing the hydraulically settable matrix of the extruded article ofmanufacture to cure, wherein the cured hydraulically settable matrix ofthe article of manufacture has a tensile strength greater than about 15MPa.
 91. A method for extruding a hydraulically settable mixture asdefined in claim 90, wherein the cured hydraulically settable matrix hasa tensile strength to bulk density ratio greater than about 5 MPa·cm³/g.
 92. A method for extruding a hydraulically settable mixture to forman article of manufacture having a hydraulically settable matrix, themethod including the steps of:combining a hydraulically settable binder,at least one aggregate material, and water to form a hydraulicallysettable mixture having a water to hydraulically settable binder ratioless than about 0.35 w/w and having an initial net deficiency of watersuch that the mixture is initially granular and substantiallynoncohesive; extruding the hydraulically settable mixture under apressure sufficient to cause the mixture to become cohesive and flowthrough a die to form an article of manufacture of a desired shape andhaving a hydraulically settable matrix, the hydraulically settablematrix of the extruded article of manufacture being form-stableimmediately after being extruded through the die; and allowing thehydraulically settable matrix of the extruded article of manufacture tocure.
 93. A method for extruding a hydraulically settable mixture toform an article of manufacture having a hydraulically wettable matrix,the method including the steps of:combining a hydraulically settablebinder, at least one aggregate material, and water to form ahydraulically settable mixture, a portion of the water being availableto interact with the hydraulically settable binder, the hydraulicallysettable binder and the portion of the water being available to interactwith the hydraulically settable binder together forming a hydraulicpaste having a water to hydraulically settable binder ratio less thanabout 0.27 w/w, the hydraulically settable mixture having an initial netdeficiency of water such that the mixture is initially granular andsubstantially noncohesive; extruding the hydraulically settable mixtureunder a pressure sufficient to cause the mixture to become cohesive andflow through a die to form an article of manufacture of a desired shapeand having a hydraulically settable matrix, the hydraulically settablematrix of the extruded article of manufacture being form-stableimmediately after being extruded through the die; and allowing thehydraulically settable matrix of the extruded article of manufacture tocure.
 94. A method for extruding a hydraulically settable mixture asdefined in claim 93, wherein the hydraulic paste has a water tohydraulically settable binder ratio less than about 0.25 w/w.
 95. Amethod for extruding a hydraulically settable mixture as defined inclaim 93, wherein the hydraulic paste has a water to hydraulicallysettable binder ratio less than about 0.22 w/w.
 96. A method forextruding a hydraulically settable mixture as defined in claim 93,wherein the hydraulic paste has a water to hydraulically settable binderratio less than about 0.2 w/w.
 97. A method for extruding ahydraulically settable mixture to form an article of manufacture havinga hydraulically settable matrix, the method comprising the stepsof:combining a hydraulically settable binder, at least one aggregate,and water to form a hydraulically settable mixture having an initial netdeficiency of water such that the mixture is initially granular andsubstantially noncohesive, the hydraulically settable binder andaggregate material together including a plurality of particles having aninitial particle packing density; extruding the hydraulically settablemixture under an extrusion pressure sufficient to increase the initialparticle packing density, thereby decreasing the initial net deficiencyof water of the hydraulically settable mixture such that thehydraulically settable mixture becomes substantially cohesive and iscaused to flow through a die to form an article of manufacture of adesired shape and having a hydraulically settable matrix, thehydraulically settable matrix of the extruded article of manufacturebeing form-stable immediately after being extruded through the die; andallowing the hydraulically settable matrix of the extruded article ofmanufacture to cure.
 98. A method for extruding a hydraulically settablemixture as defined in claim 97, wherein the hydraulically settablematrix of the extruded article of manufacture has a net deficiency ofwater immediately after being extruded.
 99. A method for extruding ahydraulically settable mixture as defined in claim 97, wherein theinitial net deficiency of water of the hydraulically settable mixture isgreater than about 10%.
 100. A method for extruding a hydraulicallysettable mixture as defined in claim 97, wherein the initial netdeficiency of water of the hydraulically settable mixture is greaterthan about 25%.
 101. A method for extruding a hydraulically settablemixture as defined in claim 97, wherein the initial net deficiency ofwater of the hydraulically settable mixture is greater than about 50%.102. A method for extruding a hydraulically settable mixture as definedin claim 97, wherein the initial net deficiency of water of thehydraulically settable mixture is greater than about 75%.
 103. A methodfor extruding a hydraulically settable mixture as defined in claim 97,wherein the extrusion pressure is sufficient to cause the hydraulicallysettable mixture to have a net excess of water during the extrudingstep.
 104. A method for extruding a hydraulically settable mixture toform an article of manufacture having a hydraulically settable matrix,the method comprising the steps of:combining a hydraulically settablebinder, at least one aggregate, a rheology-modifying agent and water toform a hydraulically settable mixture having an initial net deficiencyof water such that the mixture is initially granular and substantiallynoncohesive, the hydraulically settable binder and aggregate togetherincluding a plurality of particles having an initial particle packingdensity; extruding the hydraulically settable mixture under an extrusionpressure sufficient to increase the initial particle packing density,thereby decreasing the initial net deficiency of water of thehydraulically settable mixture, the decrease in the initial netdeficiency of water in combination with the rheology-modifying agentcausing the hydraulically settable mixture to become substantiallycohesive and to flow through a die to form an article of manufacture ofa desired shape and having a hydraulically settable matrix, thehydraulically settable matrix of the extruded article of manufacturebeing form stable immediately after being extruded through the die; andallowing the hydraulically settable matrix of the extruded article ofmanufacture to cure.